I know there are some mp themes in basic html form on themeforest right now, but not in c5 form. this is mainly so that the core team gets a cut of the sales, so they can continue developing. see this quote fromhttp://www.concrete5.org/developers/marketplace-submission-rules/...
>Please don't sell your add-on or theme for concrete5 elsewhere. We're not going to keep you from doing this legally (as Apple's >store does) but let's just be clear, that >totally screws us over and negates any value we've helped you create. The PRB is >volunteering their time to help you get the product to market. We've invested a lot in making the marketplace and the one click >install work. If you spend your energy doing a run around it really doens't help anyone. If there's good reasons for this like you've >already got a product you're just offering on concrete5 as well, that's totally cool.