I'm not sure about Limit Holdem but pokerstars does have Mixed Games Tournaments. Most of them are micro / low buyin (I guess they don't have enough interested players at higher buyins than this). I have noticed there is a number of people who regularly play in these tournaments as I've checked into them a bit myself, thinking this would be a very nice change away from NLHE for awhile and a chance to get better at the other games.