I've previously done integrations for mailchimp, madmimi and constant contact. It's all generally the same sort of functions. Since CM supports webhooks, it might be easier to write some simple HTTPPOST scripts on a webserver that will deliver data to/from CM and FileMaker via FileMaker's Insert From URL script step. Also since CM has java and PHP wrappers, you could use the free scriptmaster plugin (java) or smartpill plugin (PHP) to execute API functions from within FileMaker itself.
As for people that have done it before willing to work on it, I'm not sure what your budget is like, but I'm sure there's tons of consultants out there that are familiar with the concepts required for integration that would be willing to help you out for a fee, knowing nothing about your goals of course, I have no idea what that might cost you.
We have built a "translator" which integrates our FileMaker system directly with Campaign Monitor for a number of our clients. Primarily we have focused on both individual and group emails using a library of custom Campaign Monitor email templates. To date we have not integrated the email tracking data from Campaign Monitor back into FileMaker, but that is the next step in the process.
Please feel free to contact me offline if you wish to discuss this further.
I am interested in inegrating Campaign Monitor in my internal CRM system. Can you help ni the oe or oher way?
We didn't end up going down that route, so I'm afraid I can't help you with this. However, Paul Costanzo has integrated it successfully, so I suggest you contact him for assistance.