I have been looking into a variety of flying bases, as a result of reinterest in WWII aircraft games and a new BFG fleet. I have a mix of three options in my minis.
1. Regular 32mm and 60mm flying bases are still pretty easily available. This is the easiest option. I prefer the round stands over the hex foot versions, and these are a little more difficult to find, but they are out there. eBay is a good place to start, but also companies that make flying minis often sell the bases separately as well.
2. For my WWII aircraft, I found two sizes of brass tube, one slotting inside the other. A peg is inserted into the mini using the smaller brass tube, and the larger brass tube is mounted on a foot (I use a round 25mm base, with a 25mm polystyrene sphere cut in half, and insert the base pole into this. This means that the mini can be added and removed from the stand for transport, and is probably the cheapest but most effort required version.
3. For my BFG, I use the OmniStand from CorSec. I have the clear foot with 30 degree markings. I got a mix of the topper plugs and external mount holes, but find that the inserted plugs are pretty big and require drilling out the hole in the mini to insert. So, I have gone with the external toppers, glued to the underside of the ship and the base stem screws into this. These are pretty good, and come with a rubber washer at each end of the stem for a good fit, but they are a little fiddly. That said, they are sturdy and work well, and worth the extra expense for me in a small fleet. They are not cheap though, and in some case cost more than the Escort mini sitting at the top!