Chasing scarce or nonexistent part numbers is an interesting pastime, but it's sort of like putting lipstick on a pig. Since you've already described a perfectly viable option for getting the stick height right, why not just go ahead and do what you've already figured out works and get on to the next project? A piece of 5/16" steel fuel line that's available (or used to be) at any corner auto parts store will make a perfectly acceptable dipstick tube. Cut the tube off to the correct height to match the marks that are already on the stick.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!