It seems nfs-ganesha which used to have v2 support dropped it since then, but you might be able to compile 1.5.x release tree which is still on github.
As for patched systems, I know I have seen places which had patched images to load from, but there's non-trivial chance that they are slightly bitrotted.
Also if you can recommend me a userland NFSv2 server I'll give that a shot too.