Thank you very much. I found this timetable: http://savonlinja-yhtiot.fi/Lentokentt%C3%A4bussi%2012%208%202013.pdf , but I am going to arrive in August. Is there any current timetable?
OMG, what a maze the Savonlinja site is... As a general rule, there should be a bus service from every flight, so you can expect a connection somewhat like the "winter" schedule. I've written feedback for both Finavia (handling the airport services) and the bus company for missing current timetables.
I am not sure if that rule applies also on Kuopio because it is stated on wikitravel.org (http://wikitravel.org/en/Kuopio):
"...most flights have bus connection to city centre.".
Also I obtained some arrival instructions from a university where it is stated:
"Please note that there are no busses running from the Kuopio airport to the city centre during the evening and night time nor weekends."
I wrote to Finavia and the bus company too on Friday. So I believe that Savonian make timetables available :).
Finally, a kind buddy on Facebook provided me this link:
The bus company, which serves the connection, has been changed recently so this is probably the reason why it is a bit difficult to find the timetables...