Your wall combination isn't too obscure (toggle/toggle/decorator), so you should be able to get a single plate to do that. But if you have some other odd combinations, they can be harder to find. Hera are some alternatives:
It doesn't look as good as a single plate, but you can buy individual "gang" plates that fit together in a line. You buy the two end plates and as many center plates as necessary. Do a search for "center gang" at your supplier and you should find them. If someone went crazy and gave you a switch/outlet/dial/decorator in a row, you can build your own covers.
You can get a n-gang plate with all decorator openings pretty easily. Then, you can use inserts in them for anything else (like a traditional toggle switch).
Never used them, but found a few places easily that will sell switch plates to order. To be considered if the look of the other solutions doesn't cut it.