The Bagnall 16 inch 0-6-0 Saddle Tank, as represented by 'Empress', has never been produced in Ready to Run format: I think the closest equivalent at present, in OO scale, would probably be the recently introduced Rapido Trains Hunslet 16 inch 0-6-0, although that was an inside cylinder locomotive rather than outside as per the Bagnall:
rapidotrains.co.uk
Impetus produced a metal kit of the type, but this was discontinued some years ago.
It's nice to know that the real 'Empress' is still with us:
Introduced1954DesignerCompanyW G BagnallWeight41t 10cwtDriving Wheels3ft 6½inBoiler Pressure180psiCylindersOutside – 16in x 24inTractive Effort22,118lbfValve Gear This locomotive was built by W G B…
preservedbritishsteamlocomotives.com