Can we can certain skins in Hextech crafting?

Can we get specific skins in the Hextech crafting system that we can't get through the store or mystery gifting or is it the same for the mystery gifting, as there's a few skins we can't get because they're either had to have been in the store or you just banned them. The skins that I'm wondering if we can get are Riot skins (the ones that weren't on sale if any of them weren't, don't know), skins awarded to players like U.F.O. Corki, and skins that just can't be bought anymore like Rusty Blitz. I'd love to know exactly what we can't get in the crafting if we can't get them.

P.S. the title is supposed to say "Can we get certain skins in hextech crafting?"