The closest airports to Salla are Rovaniemi
and Kuusamo from where you can take a bus to Salla. You can see a list of airports in Lapland here
. The closest railroad station is in Kemijarvi, which has a direct bus links to Salla. You can also take the car transport train to Rovaniemi and drive from there.
You can see bus timetables and buy tickets and on the Matkahuolto website