Derby House are doing them for 1.99 in their sale section..
I use a combination of a rake and a hairdressers blade, I know alot of people clip them but to me they look horrid. I do find thogh that the finer ( more teeth) the rake the better.
Another vote for the rake - my horse hated having his tail pulled so I bought one of these and he now has a lovely "pulled" tail. You need to keep on top of it or it looks a bit toilet brushy but that's the same as if you were to clip it.