Probably Superman. Harley has run into him before, afterall.
Mechanical toothbrushes? 
Chocolate? Oh! snaps fingers, Snapper Carr-style How about new roller derby gear? You can never be too stocked up on that stuff (or so I imagine, as I’ve never participated in roller derby).
Warrior’s would be a good spot.
If you don’t know of Warrior’s, it’s Guy Gardner’s bar, which is open to all of the superhuman community, not just those associated with the GLC.
Just Imagine™…Harley finding a GL ring and the fun she’d have with it. Now that’s a great story just waiting to be told.
Hmm…
You know, I wasn’t planning on reading this right away, but since it, like the new Milestone books, is showing up on DCUI bright and early, I just might give it a gander, afterall.
Especially if it’s profane and or has the adultiness that the series has. Profanity + adultiness + HQ and friends=FUN (as evidenced by a certain TV series we’re all quite, quite fond of).