All good advice given above. I would also check auctionarms.com and gunsamerica.com data base for FFL holders in your area. If you also check completed auctions and prices at the three internet sites you can get a good idea of what stuff actually sells for. I prefer to shop local if I can, but some of the local yahoos get stupid on pricing.
FFL finder for gunsamerica.com
http://www.gunsamerica.com/FFLSearch.htmFFL finder for auctionarms.com
http://www.auctionarms.com/help/fflnetwork.cfmYou might have to register and become a member of the site to access the FFL database. There are other ones on the web also.
Might also try going to a bigger city for other gun stores and maybe even checking Cabelas, Gander Mountain, or other big box stores. Walmart does have an order book, but I don't know if they carry the SR556, but my local Walmart does have access to many other guns they don't normally stock.