If you want to find someone who specializes knows how to sell web design but don't know how to sell yourself, that's going to be challenging. Unless your projects are pretty good, you're unlikely to find someone..
Generally, I would recommend going where your target market is and do some research into who else sells to them.
For example, if you do web design for restaurants, check to see if there are industry groups or university hospitality programs in your area. Local chambers of commerce might be a good match too.
Alternatively, talk to your current customers and see how they found you. They may refer leads your way (problem solved!) or there may be a particular niche that you're appealing to and didn't even know. Then research, attend, meet, and repeat.