As VOX was the premier amp manufacturer in the UK back in the day I'd say you should have better luck on your side of the pond. IIRC the 125 cabinet had two 15s. Failing finding one, you could always have one custom made and finished in VOX livery.
I still get the warm fuzzes when I se a VOX amp, usually an AC30, on a stage.
Edit: I left the UK forty tears ago.