Supercar Engineering sells transmission parts for a rebuild/upgrade and i believe they have rebuild services. Philip, owner of Supercar Engineering, knows what he's talking about and makes some great innovative products for our cars.
although
Team Rip Engineering no longer offers services for the AWD 3S transmission, they still do have a lot of AWD transmission parts. look
look here for prices on 5 speed synchros. these are the lowest prices i've seen for synchros.