Most good automotive paint shops have the ability to airbrush touch ups. If that's all you need, it's much cheaper than an RV equipped place. A friend of mine from San Diego, just had a mobile service that often services his storage yard do a great job.
For bigger touch ups, The Paint Department in Corona does good work.
While my recent paint work at a different shop turned out well, I cannot vouch for their timeliness and cannot recommend them any longer.
2003 Alpine 40FDTS (400HP)
Long Beach, CA