Just check ebay - any that have a good amount of ratings and also ship from USA (assuming your location). There are other sim types as well - a few on Amazon- probably not a bad option since you can easily return if doesn't work for you.

I'm using a mint sim and can get everything working, BUT MMS - I think something is blocking the iPhone from getting the MMS settings that mint pushes to your iPhone. And there's no option to manually input the settings either.