Vikings didn't have horned helmets as is often depicted. Where can I find accurate representations how vikings and viking society looked?
For our purposes, there are two kinds of Vikings; western, or Norwegian Vikings that settled Greenland, Iceland, and Normandy, and eastern, or Swedish Vikings who settled Russia and the Baltic region.
There is a fair amount of literature on the first group of Vikings, who were called "Norsemen" (later Normans). One example is from Encyclopedia Britannica:
The reason is that their destiny later "merged" with that of (relatively literate) Western Europe, which kept track of them.
The eastern or Swedish Vikings, on the other hand, were less literate than their Norwegian counterparts, as is true of the lands they settled, vis-a-vis Western Europe. As a result, most literature on the Swedish Vikings is in the form of (their) "runic" inscriptions, which are the subject of study to this day.
If you are happy to focus on the military side of things, you could do quite well with some of the resources for the wargaming hobby.
Osprey books, for example, have a good reputation for accurately documenting the appearance of just about every culture's military personnel. And many of the miniature manufacturers take their cues from them or similar research.