Don't mean this in any way offensive, but what is your skill level? Do you do only photograph retouching or can you put together ads and texts, layout, visuals etc aka a graphic artist. If you can do advanced work then you're better off inquiring production houses & creative agencies, but again they probably have their own freelance pool too.
Photographers will do their own photo DI to save overheads, bigger studios and creative agencies will have their in-house dept to put together ads. Photographers in need of such service usually already have their regular contact. Why waste time & money trying someone new & untested. Also have to brief them extensively on the photographer's style etc.
If you have a portfolio, no harm presenting your work in Commercial Services Offered.