Time for an Update: It's still leak and smell free since I did it. I love it.
Most self serve wrecking yards have a few Mazda PU in them. (depending on your area I guess)
I'm a huge Haro fan myself. I feel ya on the restoration thing, except I ride the crap out of mine, lol. My buddies and I try to put about 50-60 miles a week on our old school BMXs.
Here's my '87 Sport
Do you have a link by chance?
Found it http://www.ebay.com.au/itm/Datsun-1600-Fuel-Filler-Neck-510-/281643278539?pt=LH_DefaultDomain_15&hash=item41933f60cb
Not sure on shipping to the US though.