Purchasing Missing Battle Pets: please add an option in the saved search "missing only".

Have you tried Collectionator? It provides a better UI for catching up on items you haven't collected.

Tried, but very long time ago. I prefer to use as few addons as possible, this (rumored) can improve the stability of the game. And I really like to shop through the Auctionator.

The feature isn't going to be added to Auctionator. Collectionator remains a great option, and is designed to work with Auctionator. Collectionator has been updated since you last tried it, so it may do just what you want now.