Where can you find dynamite in red dead redemption undead nightmare?

There are two ways to get dynamite, both involve saving a town under siege by the undead. Saving the mine town of Gaptooth Breach gives you dynamite, and I know there's a location in Mexico but I'm not sure which town it is.

I believe it's the town nearest to Rickets, El Matadero, but it could also be any of the settlements in Diez Coronas. The problem with this, is that you must wait until Gaptooth Breach (or the towns in Diez Coronas) go under siege, as I do not believe there are ammo crates for dynamite.