Maxol back boiler unit Mk.11/D - suitable gas fire?

We have had a Maxol back boiler unit Mk.11/D for many years and now need to change the gas fire. The last time we changed it we were told the only one we could have was a Parkinson Cowan Windsor. Years later we now need to change this again and wondered if anyone can advise us of a suitable gas fire.
Thanks, Ray