Geirfold, Blowguns were common all over Europe since prehistoric times. So it can be assumed they went in and out of fashion in Scandinavia. The first references to them date from after 1250AD when bored wooden blowguns were imported from the South. For some reason blowguns remained popular in Scandinavia after they had gone out of fashion in the rest of Europe. This may have had something to do with the availability of small game like birds and rodents.
Ah! Ok, if they don't show up until around 1250 Ad that's about 200 years after the end of the Viking Age which would explain why there are no references in any of my texts.