You could check eBay as there are frequently lots of plastic high elves for sale in large batches of 20-30 or even bigger, and they usually go for a good reasonable price. That'll give you all the archers that would you need, and if you want to convert some of the elves with blades, just start cutting up the arms to re-position them slightly, and then as long as you have one metal high elf shield already, you could make your own simple elf shields using green stuff and instant mold - there are several really good tutorials on YouTube on how to do this...
Another option would be checking the trading post here on this site looking for anyone who is looking to swap metal high elves. You may have some luck there, if you've got some items of your own that you're willing to swap.
Hope this helps, and good luck !