In no particular order;

Rare Spares

http://www.rarespares.net.au
(Exact link -> http://www.rarespares.net.au/PriceLists/Pr...its&car=115 )

Datsport

http://www.datsport.com/
(Exact link -> http://www.datsport.com/Rubber_seals.html )

Scotts Old Rubber

http://www.scottsoldautorubber.com.au/
(Exact link -> http://www.scottsoldautorubber.com.au/SUPER%20KIT.htm )

Malaysian Company

http://www.geocities.com/datsun510my/datsun510list.html

People have purchased through these guys with good results / feedback.