I was wondering if British 4’ 40w fluorescent lamps could be run on American 40w preheat fixtures. This is mainly because I like 3500k fluorescent lamps, but most manufacturers stopped making the lower cri halophosphate 3500k lamps in the 1980s. They were so unpopular here that searching for a white fluorescent lamp only yields results for cool white lamps, even though the white lamp, which was 3500k, and one of the original “white” colors, along with 6500k daylight, existed here, albeit unpopular after 4500 white, and later cool white were introduced. I have a preference for the lower cri light for fluorescents in many applications, and I know I can get them online, but I want to know if they would work here, or cause harm to the fixture.

They are the same specs, but I would doubt you will have any luck finding them either.
The reason for their unpopularity was their too low efficacy for such low CRI. With such low CRI the applications were any way reduced to places where the color quality was not any issue, but there the more efficient 4000K were acceptable too.
For higher color quality the maket just used incandescents...