There is a burial entry for William Clarke age 70 31 Mar 1851 Hook Norton but abode being Southrop which is nearby but also along Glos border area so it may be that direction to look for a marriage which I would put around 1805 when their first child appears in the Hook Norton regs:
1805 31 Mar Elizabeth d. William & Sarah
1808 26 Jan John s. William & Sarah
Couldn't see anything on OFHS CN02 covering Charlbury, Chastleton, Cornwell, Kingham, Little Rollright, Little Compton, Shipton Under Wychwood and Swerford. (I restricted my search to marriages c. 1805).
Regards
Steph