PA or Airgunproshop are the dealers for that brand. You can also try Bagnall & Kirkwood and TW Chambers and John Knibbs Airgun spares in the UK if all else fails if Ataman company direct doesn't help.
Just wondering, do you need parts due to a leak? My ultra compact just started leaking slowly; it's dropped from 300 bar to almost 160 in a couple weeks.