Seems like some suitable lapping film is included in AliExpress' 11.11 sale:
https://www.aliexpress.com/item/7pcs-set-Lapping-Film-Sheets-Assortment-Precision-for-Polishing-Sandpaper-1500-2000-4000-6000-8000-10000/32824678303.html
3 pieces Premium Quality Lapping Film 261X Precision Polishing Sandpaper 0.3mic 1mic 3mic-in Abrasive Tools from Tools on Aliexpress.com | Alibaba Group
https://www.aliexpress.com/item/7pcs-set-Lapping-Film-Sheets-Assortment-Precision-for-Polishing-Sandpaper-1500-2000-4000-6000-8000-10000/32824678303.html
3 pieces Premium Quality Lapping Film 261X Precision Polishing Sandpaper 0.3mic 1mic 3mic-in Abrasive Tools from Tools on Aliexpress.com | Alibaba Group
