In reply to ford23:
Hi,
Welcome to Norway. Whereabouts will you be?
I participate in the Norwegian skimo championships each season, so I should be able to help out.
This is the webpage for the Norwegian randonee organisation, and plans the race calender each season: https://www.skiforbundet.no/randonee/
Usually the calendar comes out in November or so.
Some races are one season only, but some are annual skimo events:
Kårvatn
Romsdal Rando
Stryn 3000
Randoenern Oppdal
Silsetrenna
Tromsø Arctic skimo
In the summer there's mountain running races everywhere. Tromsø skyrace, xreid.com, kårvatn skyrun are some. It depends a bit on what you mean by mountain running. There's lots of wilderness races too.
Most events promote on Instagram, and also Facebook.
Most events also use eqtiming.no for entry.
Post edited at 19:57