Skull White is a very fickle can of ... primer.
My advice is to go and check with a local generic modelling store. Think model trains, cars, ships and military WWII stuff.
Considering that loads of scale model kits come from Japan, they must be able to prime them there.
Tamiya makes spray cans of primer in different colours.
If push comes to shove and you cannot find a canned solution, get a cheap-o airbrush starter kit for $99 (airbrush, compressor and some accessories, not anything that uses canned air) and use Vallejo Airbrush primer. It's available in classic black, grey and white, as well as a bunch of other colours and will go further for the dollar than
GW spray cans.
Edit: Tamiya White Primer spray is article number #87044
You can see (and maybe print and take with you) the Japanese description here:
http://www.tamiya.com/japan/cms/newstopics/2145-sufaceprimer.html