Tartiflette is a recent invention. It was a marketing ploy by the people who make reblochon. So with that in mind, any barny cheese will do, preferably a washed rind semi soft. Surely someone in your area has a local artisanal alternative you could try out, or a Belgian washed would be good too.
You're looking for middish ripeness without too much "old sweat sock" association. So an inexpensive, relatively mild Camembert type with some age, or a youngish brie will be fine. If the brie is too firm to be attractive for eating out of hand, fine. You're going to be melting it anyway. TJ's rises to the occasion with lots of good choices. The ubiquitous Rouge et Noir is a good choice, too. This is for melting, not for a cheese course. Don't spend too much, a good cheese will be wasted. Again -- TJs.
I'm heading to TJ's in a little while, and will see what they have. I don't see Rouge et Noir in the cheese shops I usually frequent - probably have to go into a supermarket to find some. I love the Rouge et Noir factory and grounds. We've had many a nice picnic on the grounds, and the factory tour is and tasting is fun. My ex wife once had a surprise b'day party for me up there. Really nice, pleasant surroundings.
Yes, the dish was created in the 80s and was, indeed, used as a marketing tool. However, my research (such as it was) showed several other very similar dishes that had been around for many, many years before tartiflette. I'd say tartiflette is more a variation on some older dishes than anything new. In any case, it's an enjoyable and filling meal.
Yes, there are many local cheese makers and purveyors that might have something as a substitute. I was hoping to get some ideas sooner, however.