I'm trying to find a way to search through this forum with a search box. Am I just missing it?

You can always use Google, and restrict your search to a specific domains.
Example for looking for koolgrid event handle topic.
Koolgrid event handle site:https://www.koolphp.net/forum
You can do this in bing and google.
"Search Phase" site:Domain Url

Yup, that's what I ended up doing before I posted this. I can't say I've ever been to a forum that doesn't have search functionality.