To find Customs brokers inside the US, you can try visiting the National Customs and Forwarders Association of America's site. They have a extensive directory of brokers.
[link no longer available]
Just click the 'Find Members' tab then select 'membership directory' from the left-hand side.
Sometimes it's better to call the brokers, if you are not getting replies to your emails. That way, you will have their full attention, rather than your email being buried in their Inbox!
If you do call, make sure you have some specific information to provide them with.
I see you are interested in exporting to Eastern Europe from the US. The broker will want to know what type of items you want to export and in what quantities.