You can have a look at this app Spreadr. It helps to import products from Amazon and auto import Amazon products to your Shopify store: https://spreadr.co/
and for flipkart you can try Outlink: https://outlink.thalia-apps.com/
You can try our app to import products from 18+ websites into your Shopify store. Websites like Amazon, Aliexpress, Ebay, Target etc., Here is the link https://apps.shopify.com/alidropship
All the Best...
You can use ShopMaster.com to import Amazon.in products to your own Shopify store easily.
Try LINKIFY APP to Import products from Amazon to shopify in 1 Click.
Dropshipping (Add to Cart Button) and Amazon Affiliate (View on Amazon Button) both options.
Also they have better additional features like Auto Price change from Amazon for Affiliates, Price convertor if product is Imported from other Amazon Websites, Markup Price and many more.
Try LINKIFY APP https://apps.shopify.com/linkify