You need to spin Pokestops. They are rare, but you always gets one on your 7 day streak spin. As long as you spin at least one Pokestop every day, every 7th day you get about 15-2 items on your first spin and one of those is an evolution item. Otherwise it’s random and rare.
As far as Scyther goes, I've hatched most of mine, but also caught a few in the wild as well. You should get rare items when you spin stops or gyms for the first time on your day 7. I usually see sun rocks or metal coats when I spin on those days.