Welcome! So glad you reached out, sorry for delayed reply. Thank you for what you do for displaced animals.
EN, (Exotic Nutrition) has pretty decent cages, I've purchased two from them, very satisfied. As for their other supplies, I've purchased few other items from them over time, 2 bonding pouches, and at times their brand "HPW", specifically the "kit" which I don't think they sell anymore, not sure; and their Instant HPW. I don't recommend these for long term.
The Original HPW, now branded as Critter Love Original, would probably be your most economic choice. I'm actually on my tablet right now, or would link the site needed for the WHPS. Anyway, I've purchased mine fro Pampered Chef, maybe i can get a link in later. The fruit and vegetables are offered in recommended salads on the Critter Love official website, again, maybe I can link later. It's pricey at first, but once made your supply should last a couple of gliders for quite some time. If you want to offer pellets, not necessary, but some of us do, I recommend getting Happy Glider directly from Pet Pro website (again, sorry no links).
As for furnishing the cage, I'm not sure what was included with the reliquished gliders, but fleece is the safest and recommended material to use in their cage for bedding. Sleeping pouch would be the priority, but other fleece cage items are welcomed by gliders. You can find some bird toys and even some children's toys that are safe for them, and of course, a glider safe wheel would be the next biggest (expense wise) investment.
Being that you are a rescue, you may want to find a forever home for them, to help defer cost, you could include purchased items for sale along with adoption fees. Sugar Gliders can be quite an expense.
Wish you the best of luck!