There are at least 2-3 for sale at any given moment on G2IC, there are 3 here in my home town. I mean it's my favorite Honda and it will be the only other Honda I ever own if I ever get another, but they aren't hard to find.
It's just synchros/shaft bearings/sleeves etc. They work for both b16 and b18c trans in that kit. Are you building a 600whp car or something? For 700 bucks you can find a good working GSR trans.