Bumpers do look like old gum rubber, in an oversize version of a "T" post rubber. Could get them going functionally by cleaning up a post and trying standard rings to see what fits (stack them up perhaps). Or find something else, stacked rubber shoulder washers, or put on some sort of sleeve with a rubber ring on top.

Like to save the weird old original parts and keep them with the machine.

I've had some games which used the larger 1-1/8" balls. You could measure the old ones, and buy new from a ball bearing supplier, or a well stocked pinball parts outfit. If you check the wear marks on the game you might be able to tell if it was operated with smaller pinballs at one time.