Almost all dealers have adapters. Try
madvapes, VaporKings, LiteCigUSA, AltSmoke. All of those are reliable dealers and carry adapters. A KR808D-1 has the same
threading as a 901, and can use 901 atties, but the cartridges for 901 atties are smaller than those for a 510. You may see an adapter listed as 901 to 510, or as 808 to 510. Either will work.