There's a LFS in Halifax, NS, Canada that has had very nice Nothobranchius rubripinnis recently. They were not cheap the last time I was there, and my male killed the female (I could only afford one pair). Really, the best way to buy Nothos is via egg auctions on Aquabid, but that's harder for Americans as the best breeders offering eggs are European. Technically, you guys would need permits to import.
Unless the American Killifish Association has rediscovered the value of sharing, it can be difficult to find eggs there now. Attitudes have really changed over time.
Nothobranchius show up on lists from the Czechs, and a lot of good stores order from them. They're also increasingly on wholesale lists from Indonesia, but only the offbeat, niche farms. They come in at high prices.
Once it gets warm enough, I may spend some euros on a Nothobranchius species. I don't generally keep annual killies, but they can be an adventure.