I've never had any issues with Superlec, Electrical2go however advise things as in stock and 2-3 day delivery, most orders take 1-2weeks if you order anything that isn't extremely common as they must not hold much stock both are very cheap though.
Not much help to you but Luton town hall built 30s has lots of similar looking equipment that has long been decommissioned, same font and colour so yeah if that hasn’t been switched off for 30+ years then I wouldn’t touch it as you know it won’t turn back on!
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