Swillingtons certainly have at least been a stockist in the past, maybe worth a call.
An Ebay ad also from Swillingtons.
Mike at Brock and Norris as below in GM may have be able to help.
Mentioned “Livens” here, maybe worth a pm to DVS1
This one didn’t appear to sell on PW.
Same stock here, not clear if it sold though.
Advert from Ireland, it was withdrawn, maybe still available?
I’ll keep looking, could a 455 be modified?