Hey im not sure if this is exactly correct, but ive heard mazda series5 13Bturbo injectors are a possibility, but this may have been on a 3TG-teu.
You could maybe also try Bluewire on this forum(or u could try SA), i believe he has built a s/charged 18RGeu in his ra40, and probably has non-stock injectors and may even know the size of standard ones.
I wouldnt mind knowing either, just so i know and can have mine flowtested when they get cleaned .
id guess at them being something like 190cc but i wouldnt have a clue, just a wild guess.