I just received an email from C1. They now have a referral system. Good until May 26

Love your Capital One® card? Tell your friends and family members about our Aspire Travel™ cards and get 5,000 reward miles for each person who applies, up to a maximum of 25,000 miles1 – that’s $250 in travel! Plus, the person you refer will also get 5,000 miles once their account is opened.

You have a unique referral code in the email and thus expires May 26 ( for me).