I'm in Dallas and the local West Marine store stocked several sizes of Z-Spar Captains and Flagship varnish. I do know they have a web site which should have Z-Spar products + appropriate thinners.

Try http://www.westmarine.com/cgi-bin/ncommerce3/ExecMacro/home.d2w/report

Varnish Tips:

I found that a really good, high density bristle brush (also sold by West Marine)worked much better than the foam disposable recommended by some.

Pour a small amount of varnish into a clean container and brush from that source. Don't pour it back into the main can when you're finished unless you want to contaminate the remaining varnish with dust and particles picked up by the brush.