Paul has a unique heat sink that he is using to shoehorn the board + heat sink into the proposed enclosure. We can't find this particular heat sink anywhere...and if we can't find one neither can you. So I proposed we shift to a "C" or "U" shaped heat sink like this:

This form has a lot going for it. NFETs can be mounted on opposing sides to more efficiently spread the heat. A small 50x50 fan can be mounted at one end, and the open part of the "C" can be covered with metallic tape to help direct the airflow across the cooling fins.

This heat sink is not particularly expensive -- less than $15 from an eBay vendor. We see this type of heat sink employed in quite a few commercial EL offerings (and also in Dominik's project.) A 50x50 12V fan is not expensive (Amazon) and can generate more than 10CFM of airflow across the fins.

There is an alternative that we are exploring simultaneously -- a flat finned heat sink that is also widely available, but more difficult to provide directed air flow for cooling.

We could bend the NFET leads at 90 degrees and mount them onto the top of this heat sink, but directing the air flow is more complicated. My vote is for the "U" shaped heat sink.

Either of these heat sinks will require a complete redesign of the PCB layout. Ugh.

Paul has ordered both versions. It will be several weeks to receive the new heat sinks and evaluate their effectiveness. Everything is on hold until then.