Hi Harris
I have a few questions for you to ponder if you haven’t already done so:
Why do you want to have a presence in big retail?
What production capacity do you have?
What margin are you able to give away to the big retailers?
What other distribution outlets have you considered? Would these allow you to scale incrementally and deliver better margin?

If you are committed to supermarkets then start with New World. They are independently owned so you may be able to get placement on a store by store basis. Once you demonstrate there is a demand for your product then you can pitch to Foodstuffs to be carried as a line across all their stores.
Vicky’s comments are all good ones so make sure you have those points nailed before you approach a supermarket.

I’ve asked more questions than given you answers but without more context it’s hard to give you definitive advice.