Instead of asking for something, stand out from the crowed and GIVE them something.
Link to them in one of your posts, share something of there's on your FB profile, engage on their forums and add value to the conversations.
Helping someone without asking for anything in return is a great way to build a lasting relationship. In time, they will link to you without you even having to ask, even if you ask, at least you wont be another random in their email inbox. After engaging with them, at least they would know who you are and might respond positively to your emails.
Just remember, its not about "building" links anymore. Its about earning them!
Greg