Sort Sites based on Parent Category Chosen

Hope you are well,

I would like a plugin to nicely display my sites. I have over 100 and have pre-set categories that the sites can chose. Parent and Child Categories.

I would like a drop down accordion or drop down list to show all the stores that have that category in it. So it display to customers. See this website. How it has "find a stall" then you chose the category and the site that is related displays. I have no idea how I would begin to do this. I could do manually. But very time consuming. Just displays my business's quite nicely.

Part 2 Also I would like to have the global categories show too on the right hand side. Is there a global categories widget? Similar to this site. See how it has parent categories and then drops down to child categories.

I am using woo-commerce swell.

Any help would be great