If you haven't already, check the fuse in the L-pad on the back of the input panel. IIRC it will resemble (actually may be) a dome light bulb like you used to find in cars. These did used to die occasionally even when there was nothing otherwise wrong. Next I would call Fender customer service and see if they have something for you. If that doesn't pan out, agedhorse might have a suggestion. I think P. Audio makes an "aftermarket" direct replacement part.
SWR used Fostex/Foster horns with the plastic bell silver . Here is one from Parts Express , should fit just right . "Fostex 025H27 4-1/4" x 4-1/4" Horn Loaded Bullet Tweeter 8 Ohms" from www.parts-express.com!
"Diaphragm for Old Version 4"x10" Midrange Horn or Similar Heppner/Foster-type Drivers" from www.parts-express.com!