I've seen Steampunk submissions accepted all over the place at standard SF/F mags; as always it depends on their guidelines and the type of story they typically run.
For Steampunk-only, the options that I know of are Steampunk Tales, Steampunk Magazine, Doctor Fantastique's Show of Wonders, and The Gatehouse. I'm sure I've forgotten quite a few though.
Full disclosure: I'm the Chief Editor of Doctor Fantastique's, and I read everything that comes to our submissions email (email@example.com). We release a new crop of shorts every two months but are definitely looking to be more frequent.