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Economics Extended essay HELP!!! - Market structure issue!

Hi. Im in IBDP 1 and Im currently doing my extended essay in economics. I decided to do market structures, particularly on the oligopoly in the juice industry in my area. I have however come across a challenge regarding the data i'm collecting. The juice companies i'm investigating are the manufacturers and they don't directly sell products to consumers but rather use retailers in the form of supermarkets. I have acquired market share data for the juice companies but NOT the supermarkets. I wanted to collect primary data about prices from various supermarkets over a 5 week period and comment on the oligopoly-like nature of the industry. The issue arises in the analysis of this data. Suppose prices were to change over the time, how would I know if it is due to the retailer or manufacturer and how would I comment on it? And second, how do I make my market structure analysis focus on the juice companies and not the supermarkets?
I've been stuck for a while. Any help would be massively appreciated.
Cheers.