if you go on the orange website and do a store locator search it will give the locations for all the stores in POP etc. There's a store inside La Sirena but I don't know if they only handle sales or if they can help you with the SIM as well... at least they could provide you with the phone number and location of an alternate... I know they have a service and repair office about 5 mins from there located on Beller Street if this helps you. That office has no listed phone number so I suggest you go on the site and get the exact address and hours...
FYI if you're headed to Costambar you will pass La Sirena on your way... this is probably your best bet.
