Aliexpress
Click here… to search for Oclean P1S6 2Pcs Electric Toothbrush Heads on Aliexpress
Here are coupons that you can use.
Latest coupon and price update (UTC):
Banggood
Banggood warehouse is located in Hong Kong.
Link: Banggood product page
Coupon (11.89 USD): BG75597c
Coupon (13.15 USD): BG00c906
(CouponsFromChina.com tip: put item in your cart and apply coupon code there after clicking “Proceed to checkout”. Click to copy code and open shop)
Exclusive Allowance Coupons: https://bit.ly/3xWgD9k
Old coupons (from the oldest to the newest): BGXPAP255, BGHB218, tRaDetRaCKeR, BGHECARE1, BGf0265c, BG4ee866, Cuponation9
(sometimes old coupons work, so you can check them out (this site checks them on every price update))
Price history and price alert
Price history (for all/most countries) for Oclean P1S6 2Pcs Electric Toothbrush Heads is here.
Price records source(s): Banggood
Click on image to enlarge. 
You can set price alert (for Banggood).