Here is a website where you can perhaps start. I'm still looking for specific 'email' sites.
www.anysoldier.us/Click on the link regarding "Where to Send"
This site may have been posted before of course, but it certainly bears repeating.
Just did some more searching on that site and it appears that unsolicited email is frowned upon - from the site:
Can I email the soldiers?
More and more soldiers are getting access to email. We will not release email addresses except in unusual circumstances, and those are on the web site somewhere. We strongly suggest that if you wish to email with the soldiers that you send your email address in your letter or package and let the soldier(s) contact you.
and with regards to "getting" names directly:
Can you send me the names of soldiers who want to get mail?
No. In my 20 years as an Army Sergeant, I can tell you that I don't support this idea one bit. First of all, lists like this are usually bogus. "Soldier, sign your name on this list." Also, if a soldier is really lonely, he isn't about to advertise that. Another reason is that I have seen this backfire in a big way. A soldier's name is on a list and he has no idea that he is advertised. Worse is when his family is identified as not caring about that soldier. Not good. Let a soldier contact you if he/she wishes.