I purchase them online. I use them to make icing for my dog treats so I buy them in bulk. They're also cheaper per pound if you buy them in bulk.
www.metrocandy.com
has the cheapest yogurt chips online that I could find but when you add shipping, the price increase A LOT
www.bulkfoods.com
has yogurt bars that you can melt (they don't sell the yogurt chips). This site has the best deal that I could find because they offer free shipping (I think that there might be a minimum purchase, though). If you are looking to use yogurt chips for your dog treats, this might be the best deal. Yogurt chips aren't that cheap (from the sites that I found) and shipping can get quite expensive.
Are there any stores in your area that sell bulk candy and/or nuts? You might be able to find them in places like that. And if you don't have to pay for shipping, you'll save money