I'm not sure what it is exactly that you wish to find but your Harry Blackmore certainly put in a lot of appearences, mainly for Bolton.
Just out of general interest, there was a football who named Clayton Blackmore who was a full-back for; Manchester United, Midlesbrough, Bristol City, Barnsley, Nott's County, Rushden & Diamonds, Leigh RMI, Casleton Gabriels and Bangor City, his career started in 1983. Could he be related?