HI there – typically these stores like Warehouse have a category buyer that manages purchasing. It will also depend on where they do the sourcing from e.g. offshore and/or locally. It is not always that easy to get sourced straight away, so what I would suggest is see if you can find / contact a supplier that is already supplying these organisations and learn from them, how they do it, their margins, their process, their payments. This will I hope help you learn what you need to do to be able to not only get a meeting, but also how you need to build your proposition to have a chance.
The biggest thing you can do, is get your product into market, start selling, build reputation and get word of mouth going.