Just to clarify ... are you looking for a sgian dubh (the 3 to 4" fixed-blade knife that is usually carried in the top of the hose) or the bottle opener often found with a stag handle that is commonly referred to as a "sgian brew" and carried in place of the blade when one finds oneself in locations where fixed blades - even short ones - may not be permitted?

I have one of each. I ordered the knife from The British Shop early on in my kilting enthusiasm without really knowing much about what's available. It's one of the plastic-handled, plastic-sheathed clan crest knives with an imitation Cairngorm stone on the pommel. It holds an edge OK, but knowing what I know now, I would get a better knife with a leather sheath.

I found the bottle opener when I was at a Highland Games. I don't recall which Games nor the vendor. I've also seen combs and other non-knife accouterments handled for the hose-top, but they're much more rare than the bottle opener.

Most Highland outfitters will probably carry both. There are some specialists or hobbyists that you could order a custom job from.