Los Angeles, New York so find them with https://www.google.com/search?q=British+Betamax+tape+conversion+in+the+USA&gl=US
Once you find one, hit Yelp.com to see if they are OK. 4 out of 5 stars is fine by me as there will always be someone with bad media that the conversion house can't do a thing with.
I have a British Betamax tape recorded in London in 1986. I do not have the original Betamax player. Which USA commercial company can do a conversion to digital?