British tubes were labelled 12AX7 if they were destined for the American market, because that’s what we called that tube. The British designation was C.V. 4004, Common Valve 4004. The European designation was ECC 83. I’m sure that Brimar painted all three designations on their tubes depending on who they expected to sell them to.
Vivatubes.com on eBay has exactly what you described. I haven’t bought anything from them but they have 100% positive feedback on 21,573 transactions, so I would at least talk to them.
www.ebay.com/p/Brimar-12AX7-ECC83-Vintage-Tube/166842589?iid=153041922562&_trkparms=aid%3D555018...
Vivatubes.com on eBay has exactly what you described. I haven’t bought anything from them but they have 100% positive feedback on 21,573 transactions, so I would at least talk to them.
www.ebay.com/p/Brimar-12AX7-ECC83-Vintage-Tube/166842589?iid=153041922562&_trkparms=aid%3D555018...