The OnePlus 5T is now available for purchase in India. You can get the phone through Amazon India as well as the OnePlus Indian store. The phone costs 32,999 INR (430) for the 6GB/64GB model and 37,999 INR (969) for the 8GB/128GB version.
Source: https://www.gsmarena.com/oneplus_5t_is_finally_available_for_purchase_in_india-news-28460.php