Finally found those last three #$@%$%!@# feathers! 2 were in Venice, the third was in Tuscany. Got that achievement, along with Show your Colors, and found an easy way to get the fight 10 guards with no damage.
Get a group of guards together, any type. Drop a smoke bomb and then start shiving them with the hidden blades. Once the smoke wears off, do it again until it pops up.
Incidently with those 3 achievements done I now have a perfect 1000 of 1000. First time I've done that, though I almost got it with AC1.