There is a article on W Palmer Jones in the Shooting Sportsman(June July1989)by Ron Forsyth an australian.He notes the excellant quality of Jone's guns& his 1904 sidelock in particular.Despite this quality Forsyth says he'd seen few examples of this maker's guns in the used market. Heritage guns ( a english gun dealer has a write up on a W.P. Jones in their "sold" section.
I have a W.P. Jones 12 ga magnum from the 1930's # 20xxx)which I'm told is a very well made gun by a local english trained gunsmith
Good luck in your search

NCR