A Celica ST202 would have a harness but they are VERY different when it comes to incorporating it into the MR2 chassis. I have done it before and it's so complicated. The Caldina ST215 GT(non turbo) also has a BEAMS Greytop. Probably a bit more simple as it is more like a GEN4 3SGTE swap as they are from the same car. Wiregap could easily build you one if you gave him the MR2 harness and a Caldina BEAMS harness. Hard to find though. He might even be able to make you one from scratch.
The Altezza BEAMS engine is far too different to but useful. ECU in the engine bay, semi DBW throttle, dual VVTi. Just not worth looking at.