How to should I fill out my tcg marketplace. I will not promote

I have a marketplace startup for Trading Card Games that I have built and is solid in terms of its function. I've just recently started marketing, and have just a few real users. I feel that my crux at the moment is getting some good listings to fill out the site and make it look legit for new users. I was thinking of reaching out to vendors on Instagram and offering some sort of deal, like $25 if you list 5 cards on my site. Looking for advice on how to best reach out to people, or more generally fill out listings.