I have had many, many discussions with much older guitarists who were around in the 1950s about the availability of American instruments.
There was an embargo on imported instruments from America. We could get European ones no problem, but U.S built ones - virtually forget it. The only way possible was to contact the manufacturer directly and how many were in the position to do that? Not many - except for Cliff Richard and Hank Marvin in 1959.
Alternatively, U.S instruments occasionally did appear because of them being bought by sailors + ship crew in New York etc... and being brought back here. George Harrison's 1957 Gretsch Duo Jet was bought this way (he got it second hand in 1961). It was only at the end of the 1950's that the rules were relaxed and done away with.
We all know the first Fender over here was Hank Marvin's Stratocaster ordered directly from Leo Fender in mid 1959 - I talked to a chap who worked for Selmer in 1959/'60 - Selmer became the importer for Fender in 1960 and he had the first 'official' Stratocaster in that same year. Sunburst with a rosewood fingerboard. Cost an absolute fortune too - anyone who complains about the prices of new Fenders and Gibsons should look at back then for a reality check - it was the equivalent to about £5,000
Gibsons appeared in shops around the same time - although I have seen photos of odd models in the UK before 1960. However, they would have been brought across in 'unofficial' ways. Marty Wilde's guitarist, Big Jim Sullivan, got a '53 Les Paul Goldtop in about 1958 that was reputedly Sister Rosetta Tharpe's. Again, it was aquired in a strange way - like with most other 'UK' Gibson's of that period, no shops were involved. In 1960 he 'officially' got a top of the range cherry red stereo Gibson ES 355
I remember talking to someone about a sunburst 1959 Les Paul Standard - he recalled seeing two for sale in a London shop in about 1962. He played one - didn't like it and bought a telecaster instead. They were brand new - not second hand and still hadn't sold months later. Now look at the prices....