Get a RRA LPK with the 2-stage and be done with it. It costs more, but is cheaper than buying an LPK then upgrading later.
Try Bravo Co. They ship fast and have good stuff. Better yet, go to AR15.com. There you will see a huge number of advertisers listed all around. If you need even more, check out the industry page where they are all listed alphabetically.
Also, look at the Equipment Exchange over there. These companies also sell at a reduced price in there. There are also some smaller guys who specialize in certain things, like iron sights only or FF tubes only or LPK's and boltcarriers.....and have dirt cheap prices.