Here is a nice plastics company that I've ordered from before. I loved their 6 piece plastic cupcake holders!
Here's their portion cups:
But since I didn't have those cups on hand, I used 6 oz styrofoam cups (no 5oz avail.)
my cupcakes slid..so the first batch I cut every cup down to size..so they didn't slide..but it made them shorter.
So the next one I didn't cut the top off the cups..I just eyeballed where they sit..took the cupcake back out and poked a toothpick through the cup to act as a stabilizing "rack". Since I was still worried about the cupcakes falling. I hot glued the tips of the toothpick that stuck out the side of the cup.
HTH for those who can't find what they need in a pinch