Hi,
Aliexpress is the best dropshipping website where you can find many suppliers belongs to USA, China, Hong kong. You can have the feature to set to which country you want to ship the products and you can also filter the suppliers.
Shopify app Dropshipmate helps you to import products from aliexpress and also other 18+ websites like amazon, ebay, banggood, walmart etc., This app also specifies in unlimited products import, product reviews and Daily Auto Update/Sync. Try out this app.
All the Best...