I’ve always found that the best way to gain reliable link partners is by meeting face to face at conferences, generally I’ll do people a favour 1st whether it be a bit of SEO advice or putting them in touch with someone who is of use to them.
I think building relationships is a much better way to do it than simply asking out and out.
Build relationships with people on the forums if you can’t get to conferences and remember that asking for links should not be your starting point in the conversation. Make friends and long term lasting relationships. Not just quick wins. That is the best way to find reliable link partners. (Also make sure you have a site worth linking to).