Try 2A in Laurel. They carry a lot of Sigs and I see them in there all the time. Where I got mine.
I have one that I have shot about 3 times. I have been considering selling it recently in order to pick up a HK USP. I sold a USP years ago and I miss it. My MK25 is black with a threaded barrel as well and I can shoot you some pics of it if interested. I still have the paperwork confirming its a MK25 despite the little sticker coming off after the first cleaning. It does have the Navy anchor engraved in the side though. No use in me having a safe queen if someone else would enjoy it.