hobby shops and hardware stores typically have a bin of various sizes & shapes of "project/hobby" metals, take a piece of your broken one with you and find something that matches it - then cut length to fit, re-drill hole, spray paint black & install. prolly cost you $10

i replaced both of mine

iirc, i ended up buying several pieces of the stuff before i found a piece that i felt was better than the original, i purchased both from the local ace hardware and from a local Hobby Town location, then a friend gave me a piece he found somewhere's on the interweb which has a slightly thicker side wall than the original & same diameter - this is what i settled on using.

i don't think you will be able to have the plunger side repaired by tig welding - there are two dissimilar materials involved with the plunger thingy & aluminum tubing, if you can drive out the plunger with some luck you should be able to epoxy it into place in a new piece of tubing

OK, the tubing i finally used came from McMaster.com

part # 8978K16 x 3'

Rigid Aluminum Tubing, 5/8" Od, .555" Id, .035" Wall Thickness, 3' Length

good stuff for the application

also all in on the new playfield, have been waiting for years on this one, i hope it doesn't take many more to get it