Simon
Good taste in subject matter, as I collect this era in time specifically. As mentioned Red Lancers is a good place to start as they have about 50 figures, but Berliner Zinnfiguren in Germany has a better/more of a selection as some of the older kits are still available thru them. Michigan Toy Soldier has a good array but you kinda need to know what you looking for as the don't have a search feature on their website. One mfg not offered by the others is Russian Castings which has about eight vikings. They have most of the same as the two above, but also carry the smaller scales one of which is Krenza which has viking line that includes a pretty well detailed array of boats(3) along with cross sections of boats for small vignettes. They also carry toy soldiers, but I would only recommend Conte as they have two viking boats with about 30 or so various figures in their line. With these 3 vendors you should be able to account for about 125 viking figures, but I have been able to collect over 300 viking figures so there are other options out there. Take a look at the link in my signature as it shows some of the figures I have painted so far, also look a my vbench as to some of my more recent work not included.
Good luck and welcome to my small world.