If it's an obscure mention, it may just get lost in the reams of data and it may require pot luck to find.
http://forum.12oclockhigh.net/showth...t=Spitfire+OTU
Here's an internal link to a thread discussing No7 OTU on Spitfires, using inherited cannon-armed Spitfire Is (ex-19 Sqn, IIRC). This "defence flight"was based at Hawarden (covering Liverpool area) and was involved in a number of combats and claims.
Brize Norton does seem a little out of harm's-way, though. 2 FTS and 6MU, I'm guessing Spitfires from the MU and a mixture of pilots from both. Would it be easier to trace the cannon-Spits? Far fewer of them and see what time-line they were at 6MU?
Thinking out aloud,
...geoff