They do. Its called Unlimited, all cards are legal with the exception on Ancient Mew, and World Champion deck cards. However the combos of old and new cards are so broken, that many games either last less than 5 turns, or take over an hour. They are considered legitimate tournaments, but they do nothing to improve your rank, so most people simply don't bother anymore. They are really fun, so if you are interested in playing Unlimited tournament style, then run your own. It'll be really fun.
Sneasel- 0-140 damage T2
Slowking- Coin flip for opponents trainers, tails it doesn't work. Power is stackable
Aerodactyl/ATM Rock- Need I say more?
Baby Power Cleffa- All attacks require coin flips to use, including Collect (yes it comes up sometimes)
Energy Removal- DUH
Super Energy Removal/Recycle Energy- 2 energy go away for no cost
Computer Search/Item Finder- you have access to nearly every card, with the exception of prizes
Vileplume EX- Opponents can't use non-supporters, at all. Pokebody, its hard to deal with.
My only advice, don't try to play modified against this format.