Maybe try one of the Logitech gamepads. I think the AB,XY buttons are backwards compared to the SNES controllers. It has more buttons than you're looking for, but it's similar enough to the SNES controller, D-Pad, AB,XY, Start, Select, L and R buttons. These are closer to PlayStation controllers, but they're not far off of SNES controllers either.
Edit: You might also try one of these SNES to USB adapters, not sure how well the work, but it has decent reviews. You'd just have to pick up an old SNES controller though.
There's lots of adapters. I have one very similar to this, which was $12 when I bought it: https://www.amazon.com/SNES-Controller-Adapter-USB-Super-NES/dp/B002IXZ5DE
If you have an original SNES controller that still works well, you might do the adapter route, instead: http://www.amazon.com/SNES-Controller-Adapter-USB-Super-NES/dp/B002IXZ5DE
Or one of these from Amazon. You can connect up to 2 original SNES controllers to your computer -- perfect for playing Turtles in Time with friends on your computer.
I have this too! I also have this one for SNES
When it comes to console USB controllers, I think it's best to just get a USB adapter and an original controller instead of an all-in-one that tries to replicate the original.
I have one of these and it works fine. Just make sure that when you get the game pad, that it's an original SNES controller and not a knock-off.
No drivers needed. Just SNES controllers. Works flawlessly.