I'm pretty sure the torch is specific to that machine although possibly any torch with a gas valve built into it may work. PM weldequip on here, he's a Clarke dealer who will be able to source you a replacement.
Just out of interest, was the machine sold as 'working' or was it 'spares or repair'?
They're decent machines so if it's a runner and a keeper then it may be worth considering fitting a euro torch upgrade to it, not particularly cheap but very worthwhile on the right machine .
The seller says It's pretty well unused bar for 30 mins use. He says he pinched the torch for his bigger welder and it never got put back. I paid £181 for it...so how much I have to pay for a torch will help define whether I got a bargain or not.
If it works then you've got a good machine, I won't say it was a bargain as any machine without a torch is purely a doorstop unless it works.
A full DIY euro conversion will set you back somewhere around £90, maybe a little less if you shop around so you're looking at £270 for a very decent 150 amp machine.
Definitely send weldequip a PM, he will price you up a new standard torch for it.