Presumably you have searched the Discovery catalogue at The National Archives, at
https://discovery.nationalarchives.gov.uk ? Putting in a search term like 'besley will devon' brings up 41 entries including Besley wills held at the Devon Archives and Local Studies Service (South West Heritage Trust) at Exeter, and as well as the PCC wills which you already have. Those listed seem to be from the Inland Revenue Wills Series,1812-1857, and as far as I can remember are available on microfiche in the search room. I guess you would be interested in the copying service -details available on the website - but unfortunately that is likely to be expensive and slow.