It seems the business model of stock prop firms is based on generating revenue from commissions. You don't need to show so much ability or experience because they can keep you on a tight leash so you can't lose much money (and I understand correctly your losses come out of your "deposit").
Their most coveted traders are the ones who do hundreds of trades a day (generating huge commissions) plus make a bit extra to give them a living and keep them there.
In contrast futures prop firms revenue model is based on betterment of capital. They want traders who will generate excellent risk-adjusted returns, and will pay them a management fee (typically 1%) and incentive fee (15-30%) to do this.
Typically, you will need a 2-3 year track record with very good returns on a decent size account before they will look at you.
So, to answer your question, I think there are not too many futures prop firms because it is a totally different ballgame to stock prop trading.
Whoops, I didn't answer your question - a big one is Commodities Corporation, now a division of Goldman Sachs. You can read about them in the Market Wizards or Pit Bull. I know of others, but don't want to post them on this board. Most have relations with futures brokers. Generally, if you are a great trader they will find you.