I've had this Galvatron since 1990-something when I got it incomplete at a yard sale. Ever since I never got around to completing it until this year, thanks to ebay.
Bit the cannon barrel was impossible to find, so I decided to risk a 3d printed version through Cybertron Surgery.
(Link below)
Diorama & Display

It took a little over a month to arrive to me from Australia.
I paid for one, and got two (I suspect one was print error so I got it from free).

There was a catch, the peg was about a milliliter to wide so I couldn't attach it to either Galvatron's arm cannon, or the alt mode.

I took my Dremmel and shaved off some it and now it fits much better.

I'm a little unsure about the long-term durability of the cannon barrel; it's solid orange plastic (maybe it's painted?) I can't really tell because the flawed one had a black base color, but the good one was still orange after I shaved them both down.

It feels solid enough, and will make an appropriate substitute until I can get an authentic barrel.

Though it is nice to finally see what G1 Galvatron looked like in his prime.