The Hornady 9th Edition Manual shows various loads using A#9 with varying bullets. I cannot however find any 300Blk data on AccuratePowders site. Googling show some results/postings.
I've actually been looking into this for the last couple of days too. I use #9 for 10mm, 357 Mag, and 44 Mag already, so it would be ideal to find a good load for it in 300 Blackout. I have a little bit of 5744 that I use for my muzzleloader, so I'm going to give that a shot as well. Sorry I'm not able to help..… in the same boat. It will be nice of the powder situation ever loosens up.
Go over to 300blktalk.com I'm sure there is some info there. Some of those guys have tried about any powder you can imagine.
I just looked over there, somebody posted that it's listed under the loads for 300 whisper in the Sierra book.