Exactly that...a pulling comb...a little metal (or aluminum) comb...I like the ones with a handle for your hand to fit on...go to a tack shop and tell them you are looking for a puling comb...they will lead you in the right direction...Good luck!
You're probably thinking of the Grooma Mane Master or mane combs that have something like a razor blade built in. The Mane Master is $34.00. I've never used one, but I think that it might not be worth it for the price- there are cheaper combs that you can use that probably get the job done just as well. I've just been using a normal aluminum pulling comb.