Apexi Power FC is definately available for the MK4 Supra, I can get them no problem, in stock at my supplier in Japan, nice bit of kit for the money definately.
If you really want to go to town though forget that and go for the AEM, I have one on my car now, its capabilities are endless, I've only really just started mapping it after sorting out a few "problems", nothing serious though. My car now feels quicker than it did before on a much lower boost setting. It can also run all sorts of extras like traction/launch control,nitrous,anti-lag,water injection,etc. Nice