Late suggestion, the OP has probably resolved the original problem, but if anyone else is looking for a basic 'generic' item check out Scuba price on 5th Ave and Calle 9th (half block south towards the cemetery). Jimmy's stock is more wholesale to the shops on the island but still open to the public. He supplies a lot of the shops with masks, wet suites, fins ect. The premier shops such as Cozumel scuba repair and Pro Dive carry name brand import items and can support a diverse group of divers (and I use CSR) but that increases their costs. Scuba price carries some name brands (including JBL pole spears) but also a lot of domestically produced items. Not really 'Walmart' but more of a niche shop that should be able to accommodate most divers needs