Atticworx wheels are the only ones with the x mount.
They have a couple freedom wheels on amazon (made by atticworx ) with the x mount for about $56.00 US.
https://www.amazon.com/Atticworx-Glider-12-inch-Freedom-Purple/dp/B07QBF1F4R
Some folks love the freedom wheel because you can submerge the whole thing and clean it easily without seizing up a bearing. Others have had issues with the wheels cracking and Im not sure if they resolved that issue yet or not... There is a review that says it has been addressed and the amazon listing is the reinforced design. Its the only "safe wheel "i dont personally have.
Or the other option is a floor mount for other safe wheels like raptor, not sure if fast track has a floor mount or not, I dont remember.
If you go with a floor mount I would suggest a custom cruiser wheel. Its one of the best quality made wheels that last and automatically comes with a floor stand.
You would need to secure the floor stand to the bottom of the cage with a zipties, and make sure there is plenty of room behind the wheel and on the sides. The wheel is 6 inches off the floor for saftey reasons, other floor stands are lower to the floor.
Or you can join some facebook glider groups n see if anyone is selling stealths, sometimes vendors will buy a bunch of wheels and sell them even though they arent the maker
On a side note.. I do feel safe wheels are important... however, gliders will survive and be just fine without one for awhile if you dont have one by the time they come. There are plenty of other ways to keep them stimulated until you get a wheel ;)
I understand you want whats best for them and to give them what they need but keep in mind gliders are very adaptable and will be so busy getting adjusted they wont even notice if theres a wheel at first.