I know that the gift shop guy in Novac does, but does anyone have a list of other people who play Caravan that you can buy (items or services(i.e. repair)) from?

A quick google will do it in future, first link when i typed it in http://segmentnext.com/2010/10/19/fallout-new-vegas-caravan-cards-and-players-location-guide/

Thanks for that. That's a start. Now to figure out which ones are shopkeepers of sorts.

For the record, I did not google it, but I did try to find it on the Wikia.