Ah I see, so the two shops would share some of the products, but the price might be different?
I'm sorry, no app comes to my mind. But I'm working on building something similar. If you want, reach out via email and I'll keep you in the loop when the app is ready.
I am using Importify and I can import products from another Shopify store to mine. Aside from the 40+ wholesalers and sources, I can use other stores as long as they are using Shopify as platfrom as my dropshipping source. Of course, it is still best practice to contact the store owner and ask for permission or work out an agreement. Hope this helps!