They're going to the GSXRs for the last few years. 750s were cheap and plentiful. High performance parts available. Chopping off the tranny. Running alcohol. These guys knew how to wring out a 750. Go to a 3/4 site and ask around for parts. They are in the garages and probably relatively cheap but most have had the dog#$%* run out of them. Ask MRieck about the set of RC rods I got. $200+ wasted except for souvenirs. 2 were twisted and the other 2 not much better. He did a head I picked up from a 3/4 guy also. It already had Kibblewhite 33.5mm Black Diamond valves, springs, etc. Got a good deal but took a big chance. Mike finished that off with a few more pieces and a great porting job.
So, yes, I'm certain you can find sources within the associations. Post a Wanted listing for 750 Honda high performance parts. These guys need cash too.
Try this guy but don't buy rods

He may be able to give you some leads too.
samhankins@peoplepc.com"Hello, The head was not run on our race car . It was a stock bike head when i started with it. I did not check to see if it had been milled but it did not look like it had been to me. I do not beleve it has been. The rods were in an engine that my son ran. He got the engine in the car that he bought .We run the engine about 1/2 season and replace it with another. We had them in the cabnet for a while and desided to sell them. I had forgot even where they had come from , but my son rembered. Sam"