I went looking and you may be out of luck if still running the 630 chain. It was only used a little bit and it appears the sprocket makers may be dropping all 630 stuff since not used much to go to 530 by using '530 conversion kits'. And those don't go much smaller either on the rear. I ran the JT, Sunstar, and Parts Unlimited sprocket books to come up with that. SOHC does not fit, the hub pattern is different.
You need to verify 630 or not, measure carefully from pin center to center and 630 is 3/4" while 530 is 5/8". Each link may be stamped with it too, often done on the side of the plate if you wipe it off very well.
FWIW the '79 750F Supersport used 15/38-630 as OEM and that should be fine. Honda bike engines are nothing like Harleys and they like to spin fast all day long. You would be more likely to damage one lugging it too slow rather than spinning it.
I haven't chased sprockets in some time, the last time I looked they were available in almost any tooth you wanted, apparently today's world of much more limited inventory to control costs has changed that. I couldn't find any 30 series tooth in almost anything except very small bikes using small chain. We are now in a world where you kind of cater to the businesses rather than the other way around or the way it used to be. Take the unitized car part thing where you cannot get a simple bolt any longer, you have to buy the bigger part the bolt goes to now and often in a subassembly to buy several parts you don't need to get the one crap part you have to have. Everybody is pretty much doing that now, they don't want $5-$10 parts sales any longer, they want $100 or better if they can force it out of you.