couple trivia things to mention You MIGHT be able to search for a replacement based on dimensions alone from a bearing house with online catalog info you should be able to get at least the OD and ID (donut hole) but miaght have to guess at the thickness, however since Phil is working with you they should now that DIM. Which also means it's probably REALLY custom or they'd have already done this look-up.

Another detail I learned from MiamiJim who did the extensive how-to Wiki re: removing seals and cleaning/regreasing with bearings in place: most "rubber seals", which is the "RS" in part numbers (ie 6900 2RS. in this case a rubber seal on TWO sides) have a spring steel center which is covered with synthetic "rubber" and just the edges are thin rubber alone (not steel) that fits into the groove in the bearing housing. So Jim's advice was to use a thin but wide blade to pry JUST on the thin rubber INSIDE edge (the ID or Donut Hole, not the outside edge) of this outboard seal.

All that seemed counter-intuitive to me but...he had expertise and I only tried once (after damaging that spring steel which NO amount of blacksmithing would ever flatten out again) and his technique worked!
Blade he showed was the "mat cutter" version of one of those Snap-off type knives like an Olfa, but the size closer to a Stanley knife (but NOT as thick a blade as Stanley-type).

Some might have luck with some sort of Xacto or scalpel blade but I think a common #11 is too pointed, you want to use the EDGE to lift (not a point) and NOT to cut that edge! that's what does the actual sealing.

Find that MiamiJim Wiki and study it; then practice on a junk 2RS bearing you can afford to waste