You have to transfer NEO to the yourself in the NEO (or Neon) wallet in order to claim gas. After you do, just click the token 'claim'. https://steemit.com/neo/@jarrodcronin/a-neo-wallet-guide
video:
*Make sure you use a WHOLE number when you withdraw. But yeah, it would be easier if Bittrex just gave them out.
RE: NEO Investors Contact Bittrex ASAP and put pressure on them to distribute your rightful Gas tokens...