Mercado Central does NOT have chocolate chips, mercado central is for wholesale buyers and unless you are planning to buy VERY large quantities of fruits, vegetables, meat or fish you have to go there on a day that they sell to the public.
Aguila chocolate is made by Arcor, however they do not sell direct to the public. If you want to buy anything truly inexpensive at TRUE wholesale prices, you can only do this if you have a CUIT not CUIL and be registered as a reseller, be registered as a payer of IVA and ingresos brutos. This will give you the opportunity to buy at wholesale prices because you are registered as a reseller. Otherwise you might get a discount, but you will NOT be paying true wholesale prices which are significantly cheaper than retail.
I have chocolate chips in my shop both white and milk chocolate. They are basic quality and made by a small chocolate producer. White chocolate chips sell for $61,00 per kilo and milk chocolate chips sell for $50,00 per kilo.