Not any expert or anything but the cork sounds fine for them. As for other toys theyll literally paly with/on anything.
When i first got my gliders i also bought the fancy orange silent glider wheel(the one youll probably see adverizments for on this website) and they were not big enough to turn the wheel but they liked hanging out in it, so i ziptied it to the wall in the cage and they like to play on that.
Theres other branches and platforms that you can find online for less than $15 that work well with them, as well as running wheels thatll actually turn for them
Plastic army men or monkeys in a barrell are also good
One good homemade toy that my pets like is a wiffle ball with bits of fabric in it. Cut strips out of a tee shirt or fleece and stuff them into a wiffle ball and the gliders will love to reach in and pull it out, you just have to put it back in every night
Another toy i just got was one of those little baby tower toys. Its about 8 inches tall with a ring of every color going up, they just climb on it, got it from a pharmacy for like$8
Youll be surprized with what they find fun, just throw some * in there and watch them go nuts