In reply to goatee:
You are sort of correct in that the bus service to these distant locations ends at that time of year. At the end of the summer season the bus service narrows down to weekends, and final day is sunday Sep 4.
But by a bit of changing on destinations you can still get bus transport to another destination, Leirvassbu, close to Spiterstulen.
The bus from Oslo bus terminal Aug 30. 13.05 will arrive at Leirvassbu at 20.30 the same day.
All local bus service in this mountain area ends at Sep 4. At that date it is still possible to take the bus to Otta (via Lom) or better direct to Oslo via Fagernes.
If you insist on exstending the trip to Sep 6. you need to choose another ending, like Tyinkrysset, which has regional bus service year round.
It is also possible to hitch hike, and in that area the chance of getting picked up is reasonably good.