Nearly every widget manufacturer in my niche has an online store where they sell their branded hats, t-shirts, accessories, and everything else.
I've contacted the marketing directors from these companies, explained how I could drive more traffic to their online stores, but have been told that they don't really care about sales from their online stores.
Huh? Why have them up in the first place? They would make more profit from the sale of a single $20 t-shirt than they would from the sale of a $500 widget
Why not offer some widget merchandise by yourself? There are sites like cafe something (forgot the name) where you can configure your own T-shirts, mugs, baseball caps etc. and you link to them via an affiliate link.