I like this one the best! But I would need to add some pom-poms to the head piece. I can probably find backdrops and build a set into a short film kinda like a porno cameo.
http://www.artificeclothing.com/em/shop/Scripts/prodView.asp?idproduct=182
I've never seen a vinyl version of her costume before. I agree, that costume is definitely you! Its also pretty cheap considering how detailed it is. I just now remembered this group of people that G4 did a special on a few years ago. I'm such a retard sometimes, I can't believe I didn't think of them right when you said you wanted to dress as Harley. They go to ComicCon and dress like the Batman characters, and their outfits are great. Sorry, no Poison Ivy though. http://gothampublicworks.com/harleyquinn.html
Even though I think you should get the vinyl costume above, you'll probably like to check this out just for the heck of it. I think Harley, The Joker (Harley's husband in real life I think) Catwoman, and Two-Face look the coolest. Their Two-Face looks better than the ones in the movies in my opinion.