My first thought is, why not just plug it in via USB? Why the focus on bluetooth? I don't understand why anyone would use wireless tech, when wires are so much more reliable.
Anyway, there might be Bluetooth enabled mechanical boards. I have no idea, I've never researched it, as I have never even considered going wireless for my keyboard and mouse, but I have seen that there are adapters out there you can buy that will turn any USB keyboard into a Bluetooth wireless keyboard. (Not sure how they keep them powered, but there must be a battery or something).
Seriously though. I don't understand why anyone would sabotage a highly reliable wired keyboard, by going Bluetooth. It's such a downgrade. I don't care what it is, anything wired is always better, higher performing and more reliable than anything wireless. Doesn't matter if it is networking, input devices, charging (for power), display sharing, music, you name it. Wired is always better, unless you ABSOLUTELY need mobility.