The product you are looking for is http://blog.duncraft.com/2011/04/26/coles-hot-meats-no-squirrels-just-birds/ according to the web site its sunflower seeds that are treated with hot pepper that is supposed to prevent the critters from eating it. But according to some of the replies in their site, some folks must have Mexican squirrels as it is not working for them.
We have found the best way is to install the feeder on a long very thin wire off a pulley system. We can lower the feeder down to fill, and pull it up high enough so the critter cannot jump up or slide down. A flat dish mounted up a few feet from the feeder will prevent them from if they can sliding down to reach the feeder. Once they have to go around it, they simply cannot hang on and end up jumping down to the ground,
Another web site that offers solutions to your issue is http://www.songbirdgarden.com/store/scripts/prodList.asp?idCategory=428 Hope that helps.
There are other powdered squirrel repellents, like Hare-Less and Squirrel Away.
Here's a research paper on how pepper affects birds and squirrels. http://www.walterreeves.com/uploads/pdf/squirrelpepper2.pdf
Let us know how the pepper repellents work!
It's just dried bits of hot peppers, they dont affect the birds. Squirrels hate it though.