Find an oldtime parts man who can still read a progressive size chart- - - -the one in the back of every printed bearing and seal catalog I've seen for the past 50 years. That one will list the OD, ID and thickness of every seal the company manufactures, plus cross references to other manufacturers' part numbers. Then all you need is an accurate dial caliper and some good measurements. I'd probably start looking for that kind of person at an industrial bearing place, rather than a parts store. Lip seals aren't unique to automotive applications- - - -the same seals are used in a wide variety of industrial situations.
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!