Has anybody ever tried The Garrett GT25/40R turbo??
It looks like a direct replacement for the T25.
I found it on ebay searching for GT28RS.

Basically, the GT25/40R is really close to a GT28RS.  I'm not sure if they use the same wheels.  It's basically a T25 turbine housing mated to a T4 compressor housing.  I would make sure it has a .86 A/R on the turbine housing before buying it as you don't want the .64 A/R housing, which is smaller than stock.   :P