Hey Teva! I would do one of two things if I were you - hunt out some old slides at antique stores, or even more easily ebay (there are a TON of old slides up for sale there) and use those, or buy a cheap plastic 35mm camera at a thrift store (I can find them around me for between 50 cents to $2) and some new rolls of slide film. If you just want to make a lamp or a small project, you can get by with 1 roll of 36 exposure slide film. You don't need Kodachrome, which Kodak has actually stopped making. Kodak produces slide film under the names Ektachrome and Elitechrome, and Fuji has a bunch of different slide films available too (Velvia and Provia come to mind). If you're shooting new slide film in a cheap plastic camera in daytime, I'd stick with 100 or 200 speed film.
If you're making a bigger project, it'll be less expensive to buy a selection of someone else's slides. There's seriously a huge amount of slides for sale on ebay, and a lot of the auctions wind up going for prices that are reasonable.
Incidentally, Travis and I made another lamp out of film he shot and we had developed at Walmart (I'm anti-Walmart, but they're the only place around me that will send out slide film to be developed - I develop a lot of slide film at home, but I don't have the little cardboard mounts that surround the film).
The interior is just a Ball jar filled with a tiny strand of LED lights.
I posted a lamp tutorial on my blog here: http://goo.gl/83Zz
It's basically what I said in the original post about the lamp, but with some cutting instructions and such. I hope that's okay to post a link to!