Superflux,
When I needed to aquire these items, the Airgas in the area I was in had them in stock. I was trying to add a link to the Grainger site but it seems to be on the fritz right now. But you can try, if you go to thier homepage and do a search for "paint markers, the next page will have options and the one in the middle will say "paint" click on that and go to page 6, about halfway down the low chloride markers start.
I would think just about any welding supply would have them or could get them fairly quickly.
As far as brand, I am sorry, I did not deal with low chloride applications long enough to base an opinion on brand. I believe we used Nissen.
http://www.grainger.com/Grainger/wwg/start.shtmlJohn