I was at a wedding that had a candy buffet after the traditional cake/cookies/cordials. It was set up in a separate room so that it was a nice surprise when we walked in. Besides candy,they had a cotton candy machine and belgian waffles with toppings. The candy was displayed in metal buckets that had been "spilled" over on the table. We all had chinese take-out containers to bring our goodies home. They seemed to have a wide variety of candy:licorice,smarties,bazooka bubble gum, kisses,skittles, pixie stix, mints,jelly beans, plus a wide variety of chocolate bars.
I would think that Costco would be a good place to look for candy in bulk. Use small containers, put the display on a small-ish table (so it looks like there's more than there actually is!) and make sure the take home containers aren't too big.
Good luck. Sounds like it will be a fun party!