Make one, they're really easy and cheap. I made one in like 10 minutes last week for my 40g. The best part was drinking the Dr. Pepper =). I plan to make one when i get back from my vacation this weekend. Just google DIY CO2 generator and your good to go. Just make sure you use a bottle that is used to lots of pressure, so basically a soda bottle (not a water bottle) and be sure to use a checkvalve. Other than that, it's simple as can be. I'm also gonna try and make a diy co2 diffuser like a bell to try and keep the co2 in the water longer. gl.