Salem

I usually kill 10~15 argopelter at once
but I can't get any Unthrown Argo Branch
I knew it Spawns at ground near the player. so whenever after I killed argopelter I search my around but I can't find it
did I miss it or it's just too rare?

It's veeeeeeery rare

think bear paw rare.

Its a huge black branch on the ground right under you, you cant miss it

I usually kill 10-15 furfurs at once
but I cant get any furfur wings...

That aside as honey said once it spawns you cant miss it. Its big enough so even if your char is on top of it you'll be able to see it.