First, go to the brand or company web site (not the corporate one).
Check to see how many brand extension there are. Mars Inc, a private company, has different web sites for each of their brands - M&Ms, Uncle Ben's, Pedigree, Whiskas, etc. These all have their own web sites separate from the Mars Inc. The Mars Inc page does have a list of brands: https://www.mars.com/made-by-mars
Check Passport for any market data or analysis of the market for the product line.
You might want to each go to a local store to see product placement on the shelf (shelf space & height) and check the price. Get permission before taking a picture of the store display (you don't want to be suspected of corporate espionage). Go to specialty and general stores. If it is in a grocery store, try more than one chain in different economic neighborhoods.
Check ABI/Inform search for your brand and the markets:
Whiskas AND markets
Some brand names are regular words and can result in many false hits. For those do something to narrow it down:
Pedigree AND "dog food" AND markets
"Pedigree brand" AND markets
Collect advertisements on the web, print, and TV/cable. If you can get it, you can do radio, too. Not all stations have full recordings of specific broadcasts. Keep track of where & when you found the ad. Name the show or web site it was linked to.
Check for coupons. (Sunday &, locally, Wednesday are the big inserts & coupon days in newspapers, Tuesday is the coupon mailers)
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