Some major banks allow you to order dong in person, though they may charge higher fees and often require a few days' notice. If You Are Already in Vietnam

Buying Vietnamese dong (VND) is fairly straightforward, but the "best" place to do it depends on whether you are still at home or already in Vietnam.

You will typically find more competitive rates once you are on the ground.

Services like Revolut and Wise allow you to convert your local currency to dong digitally and spend it via a travel debit card.

Vietnamese Dong: Guide to Vietnam Currency - US First Exchange