I would say FFFg, but if you cannot find FFg, then you will have the same problem.
Try an internet search of he gun shops within 100 miles of where you live, and call them to see if they stock it. You might have to make a long trip and buy 4 or 5 lbs at a time to make the trip worthwhile. I had the same problem when I got into blackpowder shooting, but calling around found me 2 shops within 50 miles that stocked it.