I haven't fished Mazatlan, but I have fished the surf elsewhere in mexico and have heard the fishing is similar in Mazatlan. Large baitfish patterns that imitate the local sardines are what most folks use. I tie my own so I don't know any sources for flies although I have bought flies from Baja Anglers in Cabo when I was there. Flies like deceivers, surf candy, and flies of that sort and profile in tan or white with green or blue backs have done well for me.