It looks like the G Pro X keyboard has a non-standard bottom row (everything 1.25 wide except for the space bar), so that might cause some difficulty. You can find Mac command and option keycaps from a few places like WASD Keyboards, Max Keyboards (the only source for backlit ones), eBay, and AliExpress, but they're all going to be 1.25 wide. It looks like the Alt, Fn, menu, and Windows keycaps may be 1.25, but the Ctrl keycaps look like they're wider than that. It might be worth it to buy the cheapest set you can find and see if they fit. Even if you could just replace the Alt keycaps and the single Windows key, that would be better than nothing.