For the most part, an LPK is an LPK. There have been several different "brands" from CMMG, to DPMS, to RRA, etc. for sale on the EE over on AR15.COM. I'd check over there and see what you can find a reasonable deal on. Also, check GunBroker. Finally, you may want to check with Pete at LegalTransfers. He was expecting some LPKs, but I don't know if they have arrived yet.
AR15 Sales
As for the link to AKPartsKits posted above...I'll be one of the folks to chime in an recommend you look elsewhere. The price is good, but the service, timeliness of shipments, etc. just plain stinks.