This guy on Ebay seems to have a lot of obsolete stuff but his prices seem crazy. One 9c1 wiper arm for $40!! I just went to my local dealer and got a pair of those for $18. But this kit for $80 seems a little nuts.
Instead of getting the OEM ones(which when I went to a local GM dealer they were wanting $10 a piece or so) you can get a similar part from an auto parts store as its just a metal-rubber gasket like the ones used on oil drain plugs. Just be sure to get one that fits tightly over the bolts for the best seal and torque them per FSM specs. You need 2 per side one on each side of the steam pipe fittings. - Peter