A number of the parts used in this project are hard to acquire, specifically the regulator and solenoid valves. After much scouring, I decided to place an order for the harder parts from Poofer Supply and I was extremely pleased with them. I ordered the 100psi regulator, the 3/4" solenoid valves, the POL fitting, pressure gauges, LP hose, and several fittings. Not only were they very quick, they quickly replaced a gauge that broke in shipping, and their pricing was actually equal to, or better than anywhere else I could find parts. Plus, they are a small business supporting the maker community(fire arts specifically).
As I noted in an earlier post, some of the 1/4" black pipe fittings were a bit hard to source locally, though I did end up finding everything by going to a number of home centers. I'd recommend finding all the pieces you need in advance, so you can add the other fittings you cannot find to your orders. I had figured that local would be cheaper, but turns out I was wrong.
The only note I had about poofersupply is that their website order processing didn't seem to work under firefox. I had to use another browser to actually place the order.
The HSI I ordered from a supplier on Amazon, though you may be able to source locally from a HVAC supplier or repair company.
Most of my electronics components I had in parts bins, etc. I did order an Arduino Micro and large push button from Adafruit(a fantastic company). I will likely order the keyswitches from Sparkfun(another fantastic company).