Lew,
Try a copy of British army list 1930, he will in it if he was an officer.
This place has it on cd cheap.
linky
The problem with tracing from a name is will be there will probably have been several officers & dozens of soldiers called sellers. sometimes in the same units. serving in same theatres.
Personaly I have given up trying to trace people unless I have thier name & unit or the best is thier number. Even just just name & unit often produces many "multiple choice" answears.
The only firms with the information normaly market it, rather than share it unfortuanatly.{they bought it from the Goverment.}
In 10 or 20 years it might all be online for free.
Good luck.
Jonathan