No comprehensive list is complete without Hugh Toenjes "Blacksmoke" on the list. He makes a fine bbl and guarantees accuracy.
Just when I think I know who all makes bbls, I hear of another pilgrim making a few. Most of them don't have any inventories to sell from, only lists/orders you can join.
Tip used to keep a great inventory of ready-made bbls, but you'll have to call him as I heard that he told a FOF that he's not selling parts anymore, just guns. I've not been up there in a few years.