Hi Casstronaut and
to the forum.
If you have lost both keys and cannot obtain a replacement key you may need to purchase a
complete keyswitch assembly.
The keyswitch can be accessed by removing the four screws holding the end cover in place:
You may need a high wattage soldering iron to unsolder the wires from the old switch and resolder them to the new one.
Although, if you don't have access to a heavy duty soldering iron and the switches are identical, it might be possible to remove the contact cover complete with the wires and carefully swap it with the one on the new switch.
Try pulling the old switch apart first to see if it can be removed easily without damaging the cover. If you break the old switch trying to remove the contact cover I would suggest that you leave the new switch intact and find a suitable soldering iron
(or someone with a soldering iron who can do the soldering for you) instead.
Before you refit the end cover onto the battery, make sure that the cables are not under strain and pulling on the switch contact cover like they are in the above photo.
Alan