Ashley does build the stuff that AH Spares sells I do believe. Sometimes he posts stuff on E-Bay if he's got extra inventory but typically he sells wholesale only.
You can reach him as : To: ah <
ah@mgcars.org.uk> He does answer e-mail.
A post I replaced on Bugsy I. Looks like it's tough to do but isn't really. Buy a Spot Weld Cutter. Measure and measure and tack weld, fit door, support door finish weld. There is a tricky part to fit up towards the top where A-Post panel gets skinny and then goes the other direction. I simply cut the hard to fit part off. I also needed to replace the reinforcement panel inside the door in the middle of replacing the A-Post. I drilled out that piece and discovered just a folded box. Flattened out the piece with assist from my vice, made a template and cut out. Folded like the other piece, cut holes for spot welding and Bob's your uncle. Really pretty simple after all once you saw how everything was built.