Everything I've ever seen has it being an MHI turbo. The one I have has an MHI tag on it, and the numbering fits the MHI series of models. Now, it's certainly not impossible for Garrett to have built it somehow, but I'd be surprised. Given the relative age of the idi stuff, likely much larger volume of newer parts and the very specific nature of the question, I'd same it's more likely that someone at Banks got confused.
That being said, I have no idea where to get parts. Russ (Typ4) may. However, I have a low mileage (~50k) new TE06H that would be a good source for a replacement CHRA. I bought it 'new' off ebay and my suspicion is that it was a QA reject off the line as it wasn't complete and I think has the wrong exhaust housing - the original housing had a wastegate seat that was larger than the wastegate (fixed with an insert) and it seemed to spool slowly and not reach as high of boost as one would expect. Given that, I think what happened is someone put the wrong exhaust housing parts on it, but the center section should still be usable. I don't have a use for it anymore since I have the HX35 in there, but it'd be good for someone with the correct exhaust housing as a CHRA swap. PM me if you're interested.
~John