So my question is: Where can I find a proper plug adapter?
I would look at Skross products.
They they offer a wide choice of country travel adapters: https://www.skross.com/en/products/country-travel-adapters and they seem well aware of the need for grounding. They have adapters designed to support energy-intensive appliance like drillers.
Their assortment also includes truly universal (worldwide) adapters for globetrotters.