What's the easiest, fastest way to find a werewolf in solstheim without doing any sort of major quest?

There are only nine outside the main quest. They wander around as humans ("confused lunatic" or similar) between six and nine and as werewolves between nine and six.

Any idea as to where exactly I might find one? Or is it just 100% random?

connorflenge barrow and stormpfund barrow both have a werewolf.

Awesome, I'll head that way, thanks!

its simple walk around on solistem at night thats what i do and i find one every time just make sure you character is good or u have a daedric or silver weapom

You'll probably have to wait 24 hours and then return a number of times. They have a pretty low chance of showing up at their locations.