I bought them from this website. You want to get the tubes that are 1.75" in diameter. This allows about 1/8" for breathing room around the chips. I used the 6" tubes and they work great!!! The figures below are to the bottom of the cap, you could probably fit a couple more chips but then the cap would be closing around the top chips. You have to purchase the caps seperate.
http://www.jcdanczak.com/our_products/subcat_16.html <---Tubes (Remember 1.75" Diameter)
http://www.jcdanczak.com/our_products/subcat_101.html <---Caps (Remember 1.75" Diameter)
4" tube = 26 chips
6" tube = 41 chips
8" tube = 55 chips
Here are a couple pictures ripped off the thread over at scottkeen.com where I originally found out about them. The pictures below are of the 8" tubes...