Site Research Advice

I finally did it and decided to get off my ass and give this a go. I'm doing research on the product I'm aiming for but how do I find sites selling the same product?

I want to get an idea of what is already out there and where I can improve from. But I'm not sure where to find the competition, a simple google search isn't helping too much probably due to low SEO.

But if a low SEO is the cause then maybe that's just a competitive gap to be filled idk.