I dunno the story there but it is obvious its the same stuff. Almost all the same fitment guides and all in both sites. I will ask him when I get the chance but I think your right in that someone or several are marketing for the actual builders.
Note the one site is one of those places you subscribe to and take out an online store
www.stores.myregisteredsite.com this is the Pistol Packaging store. This is a domain owned by an internet service provider out of Atlanta that sells https stores services.
and then the Shamrock Holsters site is parked at its own domain,
www.shamrockholsters.com which seems to have been bought by a Bryan Christensen (who is the listed web master not the actual leather crafter)
There could even be more stores selling this wares elsewhere. I have seen this before. Interesting though isn't it? I will ask him what the deal is here as I am expecting to talk to him again in the next week or so. I do believe they are both legit and same product though.