Sierra Electronics has a few options. I saw a 30" (which I think is spozedta be best for FM) in there and one with a 90 degree hinge for folding when you want to put a cover over it https://www.sierra-mc.com/proddetail...%2F15-ANT-AMFM
And there is a 16" shorty... https://www.sierra-mc.com/proddetail...-GL18-FM%2FSAT

UNFORTUNATELY.... Diana from sales says these kits do not have the same thread that the FCB has. They apparently fit the standard 'wings. GRRRRR.
For $20 Advance Auto sells a universal stubby with 9 different thread adapters
https://shop.advanceautoparts.com/p/...990%7CL3*15435
But I think we want longer than another 7" stubby.
Somewhere out there will be one.