You could try using a site like Zillow.com, but I have found that they are highly inacurate (comparing single family homes to townhomes, etc.)
I would try calling agents who offer free CMAs with no obligation and finding agents that aren't overly pushy. Most agents would be happy to give you a free CMA for the opportunity to get your business whenever you may be ready to work with an agent (whether it is in a week or a year). Just keep calling different agents until you find the helpful one who offers to mail or e-mail it to you.
I hope that helps and good luck.