I haven't done a survey myself yet, but here are some thoughts:
If you are going to send the surveys to random agents, I would contact them before hand, preferably via telephone to let them know you are sending them the survey and tell them that you would really appreciate it if they would fill it out and return it to you. This way the agent knows your survey isn't just some random piece of mail. They then can connect it with someone real, you!
As far as posting your survey online...how about putting a copy of it on your website and then add a line in your signature that links to the survey?
I hope that helps you a bit. I am sure other forum members will have some good ideas for you! Good luck.