Does anyone know of a way to set a default subsidiary for new Locations created in NS?

Never done this before but it should Be possible with a simple workflow 1 set field value action on before record load of location record

workflow or user event script both will work. Also use beforeload instead of before submit or after submit because you will have the flexibility to change the subsidiary if required in future. On other note something like location isn't created much as far as I have seen, you could also use a 1 liner code in browser console if selecting manually is too much effort.