Regarding Vallejo, if you have a Hobby Lobby near you, they sell Vallejo paints in their modelling section. Their stock is often very fickle, however. The reason i go there is because I can use their daily 40% off coupon on any item.
Personally, I'm lucky enough to have an enormous local game store near me with enormous stock of Vallejo paints and other supplies at a discount. They have an online presence as well: https://www.atomicempire.com/