Hi and welcome
It is great that you want to find your lonely boar a little friend.
Please take the time to read these two guides here. You will find all the necessary information on what to look out for and beware of as well as some bonding videos in them.
A Comprehensive Guide to Guinea Pig Boars (includes a chapter on companionship with lots of practical advice)
Bonding and Interaction: Illustrated social behaviours and bonding dynamics (covers the whole bonding process in detail during the various stages but also includes the particulars of boar and baby bondings)
Can you please add your country? We have members from all over the world and very different backgrounds, access to vet/rescues, brands and climates. Without knowing we have to keep any advice as general as possible whereas we can tailor our recommendations to what is available and relevant for you straight away if you please add your country, state/province or UK county to location in account details via clicking on your username on the top bar. Thank you!