I think RTM Light (Resin Transfer Moulding) fits perfectly your needs,  RTM Light is intended for short/medium production scales, i think you can get something between 250 - 500 units from a single mould, and it's way cheaper than injection molding. 

The mould is made of composites, (ex. fiberglass, carbon fiber, kevlar, etc.) basically applying layers of different components such as fibers, resins, core materials, and gelcoat over a masterpiece, once it dries, the masterpiece is removed,  and the mould is ready to rock. 

Google for fiberglass manufacturing providers around your area, like Boat manufacturers, bathtubs manufacturers, custom car shop, or any fiberglass related provider and ask them for guidance.  

Once you find your provider, a masterpiece replica of the case will be needed to fabricate the mould, the easiest way to get it is using the actual case from the original computer. Perhaps you can find a second hand computer to dismantle and get your masterpiece. 

Good luck!

Molds are easy to grow. You just need some organic mater and a dark damp place. I recommend old new paper or bread. Some times you can even use things like pasta. 

Molds are easy to grow. You just need some organic mater and a dark damp place. I recommend old new paper or bread. Some times you can even use things like pasta. 

Depending upon desired strength and finish you could possible try vacuum forming (around a slightly smaller positive replica) or a GRP lay-up (on an identical sized negative).

Okay, slightly more labour intensive but possible depending upon your desired timescales/labour availability

there is an awesome guerrilla guide to cnc and casting by lcamtuf at http://lcamtuf.coredump.cx/gcnc/

If you really need to recreate the exact part, remove it from the display and send it to a shop that does silicone molds for cast urethane parts.  They can use the part as a master for a silicone mold and recreate it precisely for you in a material that will be similar.  It still won't be cheap, and they will need to remake the mold several times because silicone molds don't last that long, but it is probably cheaper than tooling an injection mold.  The one thing to worry about would be shrinkage, normally you would make the master slightly larger to account for that, but a place that does this professionally could consult you on that.

You can of course try to do it on your own but without experience and a good setup I can tell you your parts will not come out great.  If you wanted 1 or 2 parts for a hacking project, definitely attempt to do it yourself.  If you need 250 and need them to come out right, have a pro do it for you.

Another option is to model this part up in CAD and get injection molding quotes.  You might be surprised how cheaply this part could be made in China.  Ping around alibaba or look online for chinese toolers that are willing to do low volume injection molding.  You will need to have a CAD model for that and I can tell by looking at the frame it will be difficult to recreate that part precisely.  Doable if you are patient and willing to learn a decent CAD program (onshape or Autodesk fusion360 are the best free options).

Good luck!

Alex,

Thanks for the leads. Making a cast will not be simple as I do not have an original machine - and collectors of these machines will not be too eager to lend them out :)

Re injection molding - I did look at aliexpress offerings, and it seems prototype runs with plastic rather than metal molds can be OK for this type (250 units) of volume. From what I read so far, cost of about $5000 would be a ballpark figure. I am just scared as heck that the run goes wrong (likely through my fault, possibly theirs) and I get shipped 250 pieces of junk for my $5000... 

Any shops you can recommend? I realise that I will need to spend a good few weeks on CAD design. That's OK, learning is part of the fun.

Regards, Oscar.

Don't have a cheap chinese molder, but the best in the US is ProtoLabs.  If nothing else upload your CAD model to their site and get a quote, they analyze it for you and make sure it is manufacturable.  www.protolabs.com

Does it need to have the exact same shape? Using panels of acrylic cutted with a cnc rounter or a laser can make a case for that computer but it will look like made of various panels, may look even great if made with clear acrylic but not the same.

I guess I'm trying to replicate the 'spirit' of the original, not necessarily a millimeter-precise replacement part. I guess I should hone my CAD design skills and make a test run on a CNC router.

Any other suggestions gratefully received. So far, I think the plan would be to (1) make a CAD design, (2) make a test on a CNC router, (3) if the CAD file seems good, then do a small-volume injection molding run with a Chinese provider, eyes closed and hoping for the best? Any less risky options for an ignorant like myself?

I might order a 3d print before attempting to machine a prototype on a CNC, will save you money and works fine for fit/function.  Don't close your eyes and hope for the best!  Make sure you check the fit on your prototypes.  Another thing you should do is model the pieces the frame fits together with in CAD, create an assembly with your frame part and align the parts as they will fit together.  Make sure things fit correctly and do not interfere with one another.  Check online for plastic part design guides to make sure you are following best practices like uniform wall thickness, draft, etc.