Finally found a
source for the other Gradius III
orchestra hit. It's "HIT-07" on the "Vol. 8: General MIDI Sets" CD for the Akai S-3000. Granted, this was released well after Gradius III was made, but I think this sample might well have existed in an earlier Akai library that I haven't been able to get my hands on yet (such as one of the S-900/950 libraries). From what I can tell having looked through so many libraries, samples often get recycled between them like that.