Hey :)
Cheers for the mention, but no need to reinvent the wheel here!
There are numerous sites (as Mike mentioned) like this one: https://www.miniwebtool.com/random-name-picker/
Just put the list of resteemers in here and it will select one :)
steemworld.org shows the list of people who resteem a post (click on the post further down the page), and they can be copy/pasted from here.
Cheers!