I would create an account with Manageflitter and/or Followerwonk - both integrate with Twitter.

I know that many people feel negatively about Twitter but here's why it's great, especially for your quesiton:

There are no privacy settings.

Facebook and LinkedIn have tons of walls you run into while cruising around looking for potential buyers. And the other social networks are not conducive to time-effective/cost-effective networking for other reasons.

With these tools (Manageflitter and Followerwonk), you can search the bios of Twitter accounts for DPC, TPA, and any other relevant keyword. You can search within your location, or throughout Twitter as a whole. From there, the tools allow you to classify (List) or interact (Follow) them.

After that, I'd encourage you to engage them subtly, by favoriting and retweeting a few of their Tweets over several days.

Then begin a conversation with them, ideally about a mutual interest or some random thing they specify in their bio.

After a back-and-forth tweet or two, bring up your services tactfully. Ask them honestly if they need what you are offering. If they don't, maybe they know someone who is.

At the very least, you'll have a relevant networking partner/friend!

Another very valuable use of your time would be to post in LinkedIn groups. They are more professional than Facebook groups, and it's common for people to post jobs and other networking opportunities there, as well as pitch their own services. (See the lengthy URL at the bottom of this answer for an example).

Hope that helps - I'd love to talk more; there are several other ways you could go about connecting with DPC's and TPA's online.

Thanks,

Evan

http://www.linkedin.com/groups?gid=1783783&trk=vsrp_groups_res_name&trkInfo=VSRPsearchId%3A1618903721380231777057%2CVSRPtargetId%3A1783783%2CVSRPcmpt%3Aprimary