Tira here, from Shopify.
I'm here to help. It sounds like you want to showcase different vendors on your store. Is that right?
If so, here are some themes from our Theme Store that I found that may help:
The paid themes are designed by third-party developers. For any questions, you can contact the third-party developer for guidance. You can find their information listed under the "Support" section of the theme's page. Free themes are designed by Shopify. If you need support with these themes, we can help. Check out our help doc for an outline of what support is available for both free and paid themes: Support for themes.
Do you have an example of what you're looking to do?
Just to add, irrespective of the theme you opt for, you will need a Marketplace App to handle your orders and process them at the backend.
There are several apps available, but I would like to propose https://apps.shopify.com/SHIPTURTLE.
In case you have any queries feel free to reach out at firstname.lastname@example.org