Heatsupply sells (mostly?) US and Canadian products. Raijmakers, while Dutch, is pretty bad IMHO.

My personal preference these days:

https://www.crazybsauce.com/

Have you considered creating a macro in any image editor that supports macros and assigning that to a button / keyboard shortcut?

gimp certainly has macros and scripting features. Maybe this will help: https://www.gimp.org/tutorials/Automate_Editing_in_GIMP/

You can still edit a mask / selection with the regular UI, then trigger the cut/merge process you desire based on that selection.