Almost all the patches to the source code of teTeX have been integrated in the main ditribution. There is work in progress to have a repository of the source code widely accessible, but this is not so easy to maintain, mainly because the distribution is huge. Currently, not all the support files I am using are available, but you might be able to compile everything found in teTeX.
Generally speaking, I will not support fpTeX at the source level, although people wanting to enhance it are welcome. Unix uses autoconf and has only Makefile.in. I have to tweak these Makefile.in by hand to get them working. And I had to compile a lot of GNU stuff to make this running. I have taken the others (groff for example) from the Net.