At the moment the core widget widget shipped with the modeler are not fully “pluggable” and can not be copied and or extended.
Beside the core widgets are not open source. I would love to see this happening in the future.
Unfortunately you have to start from a new. Luck with the tooling https://docs.mendix.com/howto/extensibility/pluggable-widgets you can quickly scaffold a new widget and with the other public repos https://github.com/mendix/widgets-resources you might get to your goal quickly.