REI has bikes and camping equipment both. I find that their bike department is highly variable depending on where you are and what time of year it is. For example, in Colorado in the wintertime, the bike business is pretty much dead, so up there it's skis and snowshoes and hiking gear, etc.

I bought my tandem from a shop up north of here. It is not a "tandem shop" at all, but I knew the owner rode a tandem all the time, and he was in a position to recommend what tandem to buy, etc. The shop a mile from my house is a nice enough bike shop, but they seldom if ever see tandems, so they couldn't begin to tell me what kind to buy. So finding some local people that tour might be a start.

In shopping for my Sojourn, I did find that Surly does not have "preferred dealers", so any dealer can order them if you're content to buy one site unseen, for what that is worth. At that time, their web page did show the dealers who actually had some stock and stuff, and that might be one place to look.