Classic Datsun Motorsports here in CA will definitely be able to help you out. They specialize in 240Zs, but Les (Cannaday) knows Datsuns backward and forward. They sell a full rubber kit for the 240Z, so that may be what you're looking for, but I'd check with Les first.
Classic Datsun Motorsports
345 Olive Ave.
Vista, CA 92083
(760) 940-6365
There's Arizona Z-Car as well...
http://www.arizonazcar.com/seals.html