I think you just found it to be honest, there really is only one way to spell Steve.
Obviously Steven is another matter, as Stephen is pronounced the same, but to shorten that to Steph would give the girls abbreviation for Stephanie, or a shortened version of the male name Stefan. Other Abbreviations for Steven/Stephen would be Ste or Stevie.
Of course if you want to be different, and have a steady hand, you could always write it in Chinese, the symbols for Steve are
Steven or Stephen comes from the Greek name Stefanos which in Greek means 'wreath', 'crown', 'honour', 'reward'.
We shouldn't forget Saint Stephen, who is traditionally recognised as the first martyr of Christianity and many countries celebrate St Stephen's day (or the Feast of Stephen) on 26th December.