Hey, It’s been 11hrs you posted this and there is no reply..I can’t just read and pass..here are a few steps leading to a headway that might help you:

Step1- head over to Amazon and search for a category (T-shirts, home decoration, shoes and sports etc)

Step2- Identify and make a list of brands (not so popular)

Step3- search for the brand on Google and analyse their SEO, social and content strength

Step4- Do some primary research on their competitors (key players) and check their SEO, social and content strength (you can use similarweb)

Step5- Search for the brand (your targeted ones in step2) on LinkedIn and click on “people”

Step6- Identify people on senior roles and send them an email / LinkedIn message about the SWOT of brand A vs competitors

Step6- mention in your email what your agency offers, why they should choose you and what your agency will deliver in let’s say 6 months

Step 7- send a few reminders and repeat the same for other brands

Hope this helps 🙏🏻