I'd be suprised if you can find one, but if you look here [page 3] and note that the notch in the bottom of the speaker housing fits over the stock mirror arm, you should be able to figure it, the hole will be an oval roughly 4-5" wide to leave some clearance around the speaker magnet

Bill

Moved over to the Passing Lane

"When we tug a single thing in nature we find it attached to the rest of the world" John Muir
"When we tug a single thing on an old truck, we find it falls off" me
Some TF series details & TF heater pics & Rust-a-holics Unanimous parking lot