I have had the same thoughts from time to time.
I know that several years ago, one of the old iron tanks was replaced with aluminum, and to many folks, they would hardly notice the difference, except the valves on the new sight tubes are Much easier to use.(cannot find the pics)
I am guessing that the tubes were replaced on both sides at the time as they look to be in identical condition.(wish they replaced the darn valves!)
My concern has been more for protection. I would like to add a protective sleeve or guard around them. They work great, and I love having them. AYBC be danged!
Anyway, to your point, for things mechanical like this, my first go-to source is McMaster Carr. Good resource, product, price, and great service. Also, pretty good reference info as well.
Good luck. Be sure to let us know how it goes and send Pics.