I don't think there's a solution for this, judging from what I've read,
but I'm going to ask anyway.

Is there anyway for a Mac client using AFPTCP to see what the directory
size limit is on a folder? Or better yet, for it to show up as the free
space in Finder?

From what I understand the mac client will only see the mounted volumes
free space, so then is there a way to mount that particular folder as a
volume so it sees the capped free space?