For those who may be interested, I ordered some Winderosa oil seals (501415) for the injector pump of the same dimensions as the stock seals (9.5 x 16 x 4). They seem to fit well although I haven't run the bike yet.

I also found a Honda part number for a 9.5 x 16 x 4 seal (16163-KAN-770) although it doesn't seem to be a widely available part.