Well I would suggest looking around for an actual avian vet. A true avian vet will take in any size of bird for treatment and testing. If you need help finding one in your area let us know and see if we can come up with any suggestions.

As far as a medium to larger bird I would guess this would probably mean a conure or quaker size and anything larger. Some might include cockatiels in that size range but others classify them as a small bird.