The best flat spining planes (inverted flat spin) I've found are as follows and listed in order. I have experiece with all of these but I'm sure there are many others but I don't think they make planes that spin better than these.

1. Mayhem 90 size: Does the best of the bunch. Will do inverted rising flat spin. Pinwheels. Super easy.
2. UCD60: Does inverted rising flat spin. Pinwheels. very easy.
3. UCD46: Same as it's bigger brother but is more subject to wind.
4. Mayhem 40: Does them including the rising flat spin but is subject to wind. Is very light.
5. Twist: Great flat spins, it you do everything absolutly perfect you can get it to rise, some.
6. Harrier 3D 90: Does great flat spins but won't rise.
7. GP CAP 27%: Great inverted flat spins. Amazing, especially for it's size.
8. Fusion X3D 90 size: Great flat spins, no rise.
9. Showtime: Great with SFG but won't rise.
10. Velox 90 size: Great flying plane, most precise of the bunch, great flat spins, no rise.
11. EF Yak 68": Great spins, harder than above but does them nice, but no rise.
12. AirWild 29% Extra: Great spins, not as easy as the others, no rise.
13. Ultra Stick Lite 120 size: Does amazing upright flat spins, not good at inverted. Fun though.

That will give you a good place to start.

Thanks
Barry