Just off the top of my head, and it's been a while, but have you looked at Mountain Electronics for drivers in that voltage range?
I had an idea to convert a 6v lantern style battery flashlight into a low lumen <100 lumen light (which is subjective) that can have a long runtime. When I say long run time I'm talking at minimum more than 24 hours. My problem however is that finding a 6v driver to fit my needs is rare and I specifically do not want to go the lithium route as the purpose is a general use or emergency light for non-flashoholics.
Another solution that I can think of, is using those variable voltage regulators you can find on places like AliExpress or Amazon with the little potentiometers. I took apart one of those cheap LED "flame" light bulbs and found that it had DC/AC converter. Took that thing out replaced with a 4x AA square shaped battery pack from another salvaged light and put it together with a PVC pipe that fit (forgot what size) and had a battery powered camping torch. That I used as part of my kid's costume for Halloween two years ago. Since it was a pipe I couldn't say it was a Minecraft torch, but for simplicity and ease of the project, I ended up with the pipe and gave it a wood bark texture.
I know it's not really a hard solution, but you may have to look harder and really may have engineer your own solution.
Looking back at it I should have bought the incandescent Ryobi 18v flashlight too when they were on clearance. I feel like that have a lot of dead space in there to fit whatever you want. But never actually owned one so can't confirm. I took apart the LED version and with my limited skill set, the only thing I can see doing is adding GIT epoxy near the LED or edge of reflector for an after glow effect my kids would enjoy lolz ^_^
Hopefully it gives you some direction for sourcing a driver. A 100 watt LED COB I don't think runs hot (I'm no expert), but one of the things I would consider if i was doing that mod are:
-Heatsinking: Is it needed?
-Reflector: Can I mod and mount, or make one?
-Space: Dependent on what drive you find/choose
-Stock switch: Probably not an issue but keep in mind
-Purpose: Is this something worth your while, meaning is this something you want to do cause you enjoy it, or do you have a practical use? If it is for practical use you may be better off buying a new light. FYI, I run into that issue more of the time.
