~
You can get Parabellum windscreens direct from Parabellum... And just for the record, their "medium" screen is 22" tall, and their "tall" is 24". More info here:
http://parabellum.com/Super-Tenere-Replacement-Windshield-P79.aspx
Great choice! I've tried the tall Yamaha accessory shield, the CalSci medium, and the National Cycle V-Stream... And every time I have come back to using my Parabellum 22" medium screen. It's by far the best of those in terms of quality, fit, finish, and function. Much less noise and turbulence than any of of those other screens, and the finish on the edges is much, much better than the others, too.
Hope this helps!
Dallara
~