Great deal at Amazon for Castrol Edge Full Synthetic -- https://www.amazon.com/gp/product/B00JGQLZJ4/ref=od_aui_detailpages00?ie=UTF8&psc=1
Even if you get your oil changed, it might be worth buying and bringing it to the place that changes your oil. I bought 2 5qt jugs @ $19 USD per jug.
Of course Mazda doesn't "make" it's own oil as it's not in the oil refining business. Mazda outsources it's factory oil to some oil company. My belief is that it's Castrol. Has anyone looked into this?