mexican butterwort would get the job done

If you are looking for fly control, I don't think flytraps are the route to go. The flies can reproduce a lot quicker than a few flytraps will eat them. You would be much better off with something like those yellow-sticky strips that attract flies and then glue them to the paper. They will catch plenty of flies, don't need a dormant period, you can use as many as you need, and change them when they get too messy. I'm pretty sure Vesey's Seeds carries them, but probably other mail orders like Stoke's or Dominion has them, or you could phone around to a few garden centres and see if you can find them locally.

If you want to grow flytraps for other reasons, then you will find them periodically at garden centres or even in the plant section of major supermarkets. There are Canadian growers who will mail them to you, but not between Nov. 1 and early April, due to the risk of freezing. I can give you a mail order address if you need one.
-Don

I agree with Don, don't count on carnivorous plants to deal with insect issues. Use sticky fly strips instead. But get a VFT for the FUN of growing them! They WILL catch a few but won't solve your problem.

A Drosera capensis would be more efficient at catching small flies, however; as stated by the others, getting carnivorous plants just for insect control is self-defeating since insects are attracted to the plants and the plants will never be able to control the insect population completely. Get the plants because you think they are pretty and interesting rather than to do a job.

....and so would a sadistic pre-teen boy!