My LGS has it regularly. Not all that difficult to find. Perhaps your dealer does not want to stock it. I can buy it online but there is the hazmat expense.
It was listed fairly regularly until a few months ago. The usual suspects would be Powder Valley, Midsouth, Graf's, Natchez, & maybe Brownell's/Sinclair or Midway. Ramshot has been mostly available thru much of this latest component clusterf#ck. Check them regularly.