I used to make mine out of old reflector brackets. Always made them too long so that I could use my cage to carry other things, a spare tube when I had a Camelback on / a beer bottle / a tropicana shaped OJ carton / chocolate milk etc etc...
Somerset, like 'Heartbeat' with newer cars!
Retro MTB: 1992 Cannondale 3.0 Deore XT M730. 1992 Marin Pine Mountain Deore DX M650.
Retro road: 1992 Eddy Merckx Corsa Extra Telekom Shimano 600 STI. 1993 Dyna Tech Ti.
Modern: 2006 Wilier scandium Ultegra 6600. 2014 Wilier GTR Ultegra 6800.