sy, i was sick the last couple of days.
It looks like the M.E.G.A Team planned on using a Battery with crimped on holder.
something like this: https://www.batterybob.com/products/3729-cr2450-solder-pins-battery-comp-33-3/
I did not find a seperate holder, that would fit. so what i have done, i have bought this holder:
and soldered a wire which has the size of the 2 "+" Pins onto the cut-off original one.
Now i have a holder, that fits perfectly.
It's sad, that we cannot share pictures, otherwise i would have shown you my solution.
And for the switch, i went for an ALPS:
This was the only one, close enough. I had to clip away the 2 pins you normaly use to solder the switchcasing onto the pcb, because they didn't fit, but from switchlogic and the soldergrid it fits.
If you find a better switch, or battery holder let me know. Also, what i didn't find were knobs for the switch....