I've got one I don't use any more (the mare who was in the habit of getting cast is no longer with us) - I'll dig it out. If you message me your email I'll send you a photograph and you can make me an offer
ETA mine was full size but has a fair amount of adjustment, I'll measure it on its smallest setting.
Did notice this but the same one is for sale in robinsons for £52 its just out of stock so reluctant to pay that much if i can find an alternative. Thank you anyway though
An anti cast roller rarely stops a horse getting cast unless it is done up very tightly and that can cause a sore back.
You would be better getting some lengths of hard wood and fixing them around the stable walls at 3'6" and 2'9" so that he has something to push off if he does roll over.
I have one too, an all English leather hand made job by a Master Saddler but it's full size. You could easily remove buckles, shorten it and replace buckles to the size you need. If that's any good, PM me and I'll send you pics.
I'm with foxhunter here. If you stripped down an anti cast roller and saw how it was constructed, then I think you might look for another solution, like anti cast wall strips.
I really wouldn't want to sandwich my horses spine in an anti cast roller. If the strips don't work, and every dietary thing has been examined, I'd be looking at 24 hour turnout with good rugs instead.