If you are thinking about rebuilding the tranny by yourself at all, this site sells various rebuild/replacement parts for many transmission internals as well as a set of synchro to replace your old ones.
http://www.drivetrain.com/hondamaualtransmission.html
I've also seen some fancy carbon-coated synchro with hardened surface or something like that, which supposedly last longer so you might want to look into that as well.