Have you tried on Ama-zon or Aliexpress?

An Xiaomi Power Bank is perfect for your needs:
Specifications:
Product name: 20000mAh Xiaomi Power Bank 3
Battery capacity: 20000mAh 3.7V (74Wh)
Battery type: Li-polymer Battery
Input interface: USB-C
Output interface : USB-A / USB-C
Input: 5V 3A / 9V 3A / 12V 3A / 15 V3A / 20V 2.25A
Ouput: 45W MAX
USB-A (Single port) :5V2.4A / 9V2A / 12V1.5A
USB-A (Double Port) :5V3A
USB-C:5V3A / 9V3A / 12V3A / 15V3A / 20V2A
Three Port:5V5.4A / 9V3A / 12V3A / 15V3A / 20V2A