Were these only available in the UK or Europe?
USA back then was a hifi power house, we didn't need no twee little British amps
The few that made it over will likely cost you 3X what they cost in UK, could be worse you could be in Japan. Get a UK PFMer to grab you one, box it proper, and ship it over, but it's so hard at this point to find anything of any sort vintage that hasn't already been restored, often badly and too expensive, or been through too many hands and dubious. The mint stuff goes to Sotheby''s now.
That's why if you find something even if well worn but intact it's best to leave it as is, other than dead mint untouched honest wear and original patina commands the highest price these days. Motorcycles, cars, guitars and amps, bicycles, furniture, restored is a tier below worn and untouched now. It's not really a shabby chic, distressed, old-timey-trust-funder, fad either, it's just the rarity at this point. No more barn finds as there are no more barns, it's all been turned into condos and malls. This is maybe the last decade were something old of quality shows up untouched.
Old geezer in town has a Moto Guzzi V7 Special, one of the earliest ones, that he's been Sunday driving since he bought it new 50 years ago, perfectly intact and maintained, every part well worn but undamaged in any way. If I had any money I'd offer him
whatever he asked for it and continue riding it just as is. I bet someone stops him three times a day to ask if he's willing to sell it. If it was restored people would say super nice, but they wouldn't gush over it.