Source for D2 S8 caliper seal kits?
 

Audi Part# 4D0698471A

Dealer said no one in the country has them. ECS is backordered. Can't find them anywhere else. Is there a non-Audi part number, like from Brembo themselves?

For the 4 piston Brembos.

Edit: found my answer and adding info for future searches.

The D2 Audi S8 caliper is technically the Brembo F50. It has two 44mm pistons and two 40mm pistons. The replacement seal kits are

143.99040 for two 40mm piston seals/boots
143.99044 for two 44mm piston seals/boots

These are sold all over the place, and cheaper than the kit from Audi. The Audi kit does include new pistons though, so there's that.