Hi there!
I'm using the Platform for some years, and I see it's changing but the dialog window for getting new apps is still without any search box, however it got 10 categories there and 200+ item which are hard to find quickly when you need it.
Dialog window of PA Updater (aka PA Directory) is shown below
https://vgy.me/kmDfl1.png
Hope it would be invented in the future releases of the Platform!