VKB curved extension, which fits their base and not Warthog's. Intermediate height. Not tall enough for a floor mount
Rainman's floor length, curved extension for the Warthog. Pricey.
If you want to build one, I've been looking at some interesting ideas:
Bend steel electrical conduit with a conduit bender. You can rent the bender and steel conduit is not expensive.
Bend plastic electrical conduit with a Pipe Viper. It's a heavy spring that goes in the plastic conduit and allows you to bend it without kinking or cracking. Plastic conduit and the Viper are not expensive.
Curved electrical conduit from a home improvement store. I found two 45 and one 90 degree bends gives you a curved joystick which only needs a little cut off the end. There's also a 30 degree forward leaning Warthog joystick adapter on Shapeways. All are inexpensive and just require glue.
I tried a floor mount and settled on a 200mm extension for flying airplanes rather than a floor mount. Too much movement for full control deflection. But, I use a floor mount, curved, spring-less joystick for helicopter flying which doesn't require full deflection and needs finer control inputs.