If the store of your choice offers FLAC as an option (and I think they all do), you can simply make your own MP3s from the FLAC files. That's one of the biggest advantages of lossless audio. (The improvement in audio quality is actually pretty minimal, for most people.)
You can also keep the FLAC files to convert them to some future format later, or even do something really wild like burn them to a CD or something.