Hi im a  lv 35 horde and have got 225 cooking skill where do i need to go to get the next level cooking

Tanaris quest i believe you need:
12 Giant Eggs which are found on the Auction House or off Owlbeasts (Hinterlands, lvl 42-44)
10 Zesty Clam Meat which are also on the AH or drop off turtles at Steamwheedle Port (Tanaris, 49-50) or Raventusk Village (Hinterlands, 40-41)
20 Alterac Swiss sold at the Caverns of Time from Galgrom

As the above guy says, you need to do Clamlette Surprise from the butcher in Gadgetzan: http://thottbot.com/q6610

You can also get the Alterac Swiss from the cheese vendor in Stormwind.

also have cheese at hammer falls now

You can get the alterac swiss at Freewind Post also  34s

I found some at the Inn in Thunderbluff... I'm only 34 though.. can't do quest quite yet.

Yes he is in the Inn in Tanaris.. wont give the quest until lvl 43..this will allow you past cooking 225

Just to clarify a little. You can get the quest when your character reaches lvl 35 and has cooking lvl 225. The lvl 43 referrence is wrong. I just did the quest with a lvl 35 hunter.