Can you please tell me where can I find high voltage ac / dc converters?

As far as I know, such equipment is not used in everyday life. It is only used in specific areas such as mining, aircraft, or the military. Therefore, you will not find this in ordinary stores. So, I would like to recommend this emi filter for power supply https://www.aeps-group.com/pcategory/ac-dc-en/ , and I think that it those what you want to find