Good question.
We've compiled an impressive list of online stores for product sourcing. These stores are scanned by Tactical Arbitrage portals.
Click the link below to see the list. The list is not complete. It grows and grows!
In addition, Tactical Arbitrage boasts a feature that allows you to (with a little coding know-how), add your own sites to scan over and above the built-in options.
If you would like access to the site before it can be added to TA, you could look into having an Xpath file made for the site and added to your TA account.
Reach out to support at support@tacticalarbitrage.com for more detailed information about the recommended Xpath.