I am helping my Daughter-in-Law research her ancestors which include several John Holme's or John C. Holme's back to 1810 in Lower Dublin Township in Philadelphia. Like you I don't think Thomas Holme, the Philadelphia surveyor, had any male descendents in the USA, but there does appear to have been a John Holme in the Philly area about the same time as Thomas. Perhaps Thomas' brother/cousin ?
I'd be interested in exchanging data. If you're also interested, please contact me.