Find a couple of matching bowls of similar sizes at the dollar store or party store. We found some nice, rigid, squarish shaped ones with cutouts in the corners at our Party City store. I liked them because they were kind of modern looking (not cheesy plastic trying to look like cut crystal) and came in several sizes in the same shape. I got three of them: one each in 12", 9", and 6" diameters.
What we ended up using for our project was a container that held Kraft Parmesean cheese. It's a plastic cylinder about 8 inches high by about 3 inches in diameter, and it was almost empty, so I put the cheese in a smaller container, pulled the label off, and cut off the threaded end at the top where the cap was, and the bottom, so we were left with a clear plastic cylinder. Other options would be cake pillars (to separate layers in fancy wedding cakes and such, available at craft stores), or what I originally intended on using was a section of PVC pipe, nicely cleaned and painted with food-safe paint.
I spent a lot of time looking up pumps for this application - I wanted to make sure it was food safe, waterproof, etc. My findings were: While it would be nice to have an in-line pump to make the workings of the fountain more invisible, I went with a submersible pump. Not only was it easier to get, I was also able to make sure it was thoroughly clean, and submersibles are going to make less noise than inlines. Go to a pet store, home improvement store, hydroponics store, or garden store and ansk for a small fountain or pond pump. I over paid for mine at $25, but I was in a hurry and the pet shop was on my way home.
Please be vigilant on what you use here. I used "KwikPlastik" plastic repair epoxy putty by JB Weld. The main thing is that you need something that will glue your pieces together, but also be somewhat flexible and water tight, and food safe. We have tons of tubes of silicone sealant already at home, but I went out and bought this stuff since it is specifically "safe for potable water" where as most of the tubes of silicone caulk I already had at home had all kinds of non safe warnings on them. The tube of JB Weld that I got was about four bucks at Home Depot, and we have a lot left over.
Here's where the fun part comes in. If you don't already know this: be aware - the quinine in tonic water glows under UV light. So how about our punch bowl holds gin and tonic, or a tonic water punch?!? Go to Radio Shack and buy a few Ultraviolet LED's and some 9V battery connectors. Hopefully there's already some electrical tape and stuff like that at home. Lighting is completely optional, and you could always substitute other colors, leds, do an array or whatever to make your punch bowl to your taste.