I just come across a guy here in Texas that takes old tube PA amps and modifies them for harmonica. He's played harp for years and has been experimenting with amps to come up with the right combo for harp. I've bought two, a 12-15 watt based on a Fender Tweed Deluxe and a 25-30 watt based on a Fender Tweed Pro. They are both kick-ass. He also repairs and modifies amplifiers.
His name is Dan Moser and can be contacted at: mrharp@gt.rr.com
For an amplifier set up for harmonica, these are priced very reasonable. He also builds combos, all new, from the ground up. I drove down and picked up my second one a few days ago. He has some 12-15 watt amps ready to go.
I believe my search for that certain amp is over. I know my wife will be happy to hear that.