If the muster rolls for Dorset militia still exist they will be in the National Archive at Kew. However, whilst searching for Dorset militia records recently I made the worrying discovery that much of the Dorset militiary record was pulped in 1928 after it had been rendered irrecoverable by a leaking roof at the store.You could try Dorset on line parish clerk if you have not already done so. Though the summary page gives no indication of militia records, the clerk might know something.
