Rock Auto says they have them. SBP 10" Rear Drums -- they don't have the Darth Vader helmet flanges like the originals, but they are a good fit on my 72 swinger with SBP 7.25" rear.
If you need them, get them now. Rock Auto let me put 7 in my cart and said that was all that was available (I emptied it , so it's not "holding" any). Summit had seven a couple of weeks ago, and now they are out of stock.