Aliexpress
Click here… to search for Xiaomii USB Type-C Male to Micro USB Female on Aliexpress
Here are coupons that you can use.
Latest coupon and price update (UTC):
Banggood
Banggood warehouse is located in China.
Link: Banggood product page
Coupon (2.47 USD): BGXMI15
Coupon (2.62 USD): bGhOnEy10
(CouponsFromChina.com tip: apply code in your basket (cart) after clicking “Proceed to checkout”. Click to copy code and open shop)
Old coupons (from the oldest to the newest): 502C6B, AFfbG10
(there’s a little possibility that old coupon will work)
Price history and price alert
Price history (for all/most countries) for Xiaomii USB Type-C Male to Micro USB Female is here.
Price records source(s): Gearbest, Banggood
Click on image to enlarge. 
You can set price alert (for Banggood).