This isn't necessarily a punch, but it's a recipe for a higher quantity of juleps: http://www.foodnetwork.com/recipes/sara-moulton/the-perfect-mint-julep-recipe/index.html

This is what I did at a party: pre-mix your julip base, put it in carafes with buckets of ice next to it. Let people put ice in their glasses and pour their drinks. I had two different drinks mixed up and backup in the fridge. If you have to top anything off with bubbly, keep that separate. If you need to, you can post a small sign telling them to fill with ice, then the drink, but I think people would get the hang of it soon. Keeping the ice separate also helps keep the drinks from watering down during the event.

I have had a Mint Julep Iced Tea before that was very good. My friend actually bought a Mint Julep concentrate that had instructions to make the iced tea as well. I found this recipe that sounds good as well: http://www.myrecipes.com/recipe/mint-julep-iced-tea-10000000346753/