Write an e-mail to Sideshow Collectibles. They are actually in the process of offering prints on their website, although this one is not available (yet? not sure). Of course, please understand that Sideshow doesn't own the character of Harley Quinn, and any potential print sales need to be negotiated with DC first. So, maybe, in 10 years, you can get a print of this. : ]
Thanks for the interest though! I would totally sell you a print myself if I were allowed to.