Those type lamps are very familiar to me from my cycling days as a kid. This is the type of battery I was forever buying, but I can't say I've seen them around in years. You will probably have to just wire in a suitable capacity battery to suit your bulbs. Ron
I just did a bit of googling out of interest, and found this thread which shows an adapter is/was available to take two standard batteries.
https://rustybikebell.wordpress.com/...classic-bikes/