I assume that this has sold considering it's showing as zero stock and has done since release on the Locomotion website.
Despite appearances, I suspect that's highly unlikely. I just added one to my basket successfully, and walked halfway through checkout to test it. All successful.
I imagine they've simply omitted so far to tell their stock system how many they have, perhaps whilst they sort preorders out.
If you want one, I'd say go ahead and buy one. They'll soon refund you if I'm wrong (they're a reliable outfit)