Fragments drop from "The Evil in Stonevale" quest bosses. These include Fellfire (giant red wisp), Chillmist (giant blue wisp), Starspell (giant white wisp), Spirehoof the Corrupted (giant white unicorn) and Falgren Bloodbinder (giant red druid). I would say you could be capable of a Fellfire or Chillmist boss fight, but if I were you I would wait until about 70 for Starspell and 75 for Spirehoof. (Probably 80 for Falgren) Anyway, your best bet would be keep training, level up, and
make friends to help you get in the groups. Somebody else can post a screenshot as to where they spawn
Here is an approximate chart of what each boss drops.
Fellfire - Drops mostly moons, sometimes suns
Chillmist - Drops moons, suns and rarely oaks
Starspell - Drops oaks, elms and rarely crowns
Spirehoof - Drops oaks, elms and rarely crowns
Falgren - Drops dragons and crowns [quick note here, you probably won't get in a Falgren fight for a while since quite a few people greedily camp him all day (here on Epona at least)]
Hope this helps!
Thanks for reading,
Blazedawg