construtivst is darker i think and its a frost while quite natural is a matte. Dont they still have quite natural up on the mac website? i think its a permanant product? If not i think mac's bamboom paint is similar
I don't know of any dupes but if you can't find it on maccosmetics.com, you can get it from allcosmeticswholesale.com. I think quite natural is a pretty unique brown and I haven't seen any dupes of it.