After signing into aitp.org, on the left hand side of the page click the "Refer a Friend" link.

Your Referral Direct Link is displayed and can be copied to anywhere HTML links will work.

If your link does not contain a public key, click the "get new public key" link. For example, your public key will be after the ref= part of the link and appear similiar to the example shown below.
http://www.aitp.org/general/register_start.asp?ref=AAAAAAAA-BBBB-CCCC-DDDD-EEEEEEEEEEEE

Now use that referral link on your blog and in tweets and emails to other technology folks.