Does anyone have any recommendation for three gliders? Where are the best places to buy?

ebay has good bird cages.
also, basically, if you search on google or something, you'll find a bunch about bird cages, including places to sell them.
for three gliders, i'd reccomend a cage at least 4 or 5 feet tall.
also, reptariums are very cheap if your on a budget. you can get a lot of space for a low amount of money. i have a reptarium as a permanent cage, myself. super easy to clean, just toss the mesh in the washing machine.
now, if you want to know where to buy reptariums, the place i trust most (because its from an actual pet store, not someone who makes them by hand or something ;; made by petsmart) is here

by the way, i have the 260 gallon, which would house about 3-4 gliders perfectly.

I'd have to say to go with the Reptarium. They are very nice looking, very light weight so you can move them around with ease (great for cleaning time.) And you can't beat the space it provides for the money!
You'll need a more creative approach to designing the cage but don't let that hinder your desition.

My favorite cages are from K&D Exotics . I have my pair of boys in the 5' tall cage but three gliders would fit just fine.

It's black PVC coated and comes with a bottom grate and drop pan. You do have to assemble the cage but I think it is well worth it. I plan to get another one soon to house my younger boy and girl when I put them together. I've had my current one for almost two years now and it's still in perfect shape. <img src="/ubbthreads/images/graemlins/thumb.gif" alt="" />

Lisa from SunCoast gliders sells great cages!