As usual you've been let down by the Shacks uneducated staff. Their advertising claim: "You've got questions, we've got answers" is seldom true as you found out. When shopping the shack you need to look at the catalog (do they still have one?) or the website first, find the part number and say "give me x amount of this stock number" to the shack "rep". Here is your part number: 278-311 a pack of color coded(black/red) spades for 10-12 gauge wire. $5.99 for an 8pk.
Here is a link to it on their site: http://www.radioshack.com/product/index.jsp?productId=2103477
Here is a link to it on their site: http://www.radioshack.com/product/index.jsp?productId=2103477