As of this writing still available from Honda
91203-950-003 OIL SEAL (30X55X10)
http://www.partzilla.com/parts/detail/honda/HP-91203-950-003.htmlNOTE
To replace both crank seals you have to split the cases and remove the crank bearings their is no way to remove the crank bearings without stressing the balls so BOTH crank bearings need replaced when replacing the crankshaft seals.
If your crank seals are leaking you will need two new crank bearings and both seals and a full Engine gasket kit. Mutt on ebay selling both seals for $34.99 you can buy both for $18.28