Quote Originally Posted by robs5230 View Post
All the Theoben break barrel rifles, were fitted with the Evolution trigger from 1994 onwards
You should be able to get a date on yours (approx) from the serial number database. Message "The Squire" on here who should be able to help you date it.

Parts wise, I think the only source, outside collectors / hoarders, of Theoben parts, would be Impact Airguns / Selective Arms, who took over the remnants of Theoben's business
I don't quite understand your description of the adjustment screw. I don't believe there is a slotted screw on a theoben break barrel. There is a grub screw with a 5mm or so hex then inside that which you won't see easily is a much smaller hex screw that can be altered to increase or reduce the spring pressure against a small ball bearing held in the end of the larger grub screw. Turning the larger screw alters the crispness of the second stage.