You can buy the abrasive at any hobby or craft store.  Glass etching compounds contain hydrofluoric acid, an acid that eats through almost anything other than plastic. When you apply it to your lenses it will eat through any coatings but will leave the plastic lenses completely intact.  You will also need rubber gloves when applying the abrasive, so buy those too if you don't already have some.

TL;DR in Vietnamese:
Mua hóa chất khắc thủy tinh thường được dùng trong nghệ thuật.