Can I get an auxiliary keyboard for my MacBook Pro?

With a USB-C to USB adapter, you're set to go. Assuming the standby KB has a USB-A cable. "USB" alone is the common terminology for USB-A.

Apple sells one: https://www.apple.com/shop/product/MJ1M2AM/A/usb-c-to-usb-adapter

This assumes your MBP needs the adapter; you didn't supply year or other details. It is always a good idea to have a USB standby KB.