That looks like a 3-wire grounded power receptacle. Any change you can find the service or user manual for the device. It might list a part number.
The HP cord you showed looks a lot like the Victor-branded power cord used on a 1970's vintage Heath Kit IO 4253 oscilloscope, The line pin spacing is about 0.45" and the center ground pin is offset by about 0.15"
https://www.google.com/search?q=grou...6dw0gy8dWMWrhM
https://www.amazon.ca/Tektronix-Fluk.../dp/B011CAFR3Q
I saw one on ebay for $49.
Finding one will be difficult at best, and being sure of the fit before you buy is an issue as well. It might be lower end cost, and faster, to replace it with a more modern connectors, possibly hard wire in a proper 3-wire cord..