Greetings,

Hoping you are in the best of your health amidst this pandemic. Coming to your question, following are 3 avenues to buying an e-commerce site:
- Shopify Exchange if a marketplace you can use to buy the said business.
- Flippa - Auction sites, where you can go bid for an online business for sale.
- Online business brokers namely Digital Exits & FE International are helpful.
- Contacting Online Business Owners Directly is the last option. While you do that, it would be nice to a bit of research using tools like Alexa, Ahrefs, and SEMrush to get a more behind-the-scenes look into the health of the business.

Another good site for you to refer is
https://exchangemarketplace.com/
And
https://feinternational.com/

Lastly go through the link below which you some good 10 market places to buy e commerce business.
https://www.practicalecommerce.com/10-marketplaces-to-buy-and-sell-ecommerce-sites

I have personal experience of selling a business. Feel free to call me, in case you looking for some advice on how to pick a good ecommerce site, the salient points to confirm before buying. Such as focussing on profits than the 7/ 8 digit GMV is critical. Vendors and brokers like to push the turnover figure because it looks impressive.

You can reach me here...
https://clarity.fm/simkicity