Where do I buy wrenches I cant find them?

The wrenches / Tools for repairing your APCS are only available in the store for real money.

There should be a packages that contains them, although sometimes its not easy to find.

I have found it today in the Gift Sore under the 'Hot Package' section. Swipe through to find APC Durability Recovery

The quickest way to find the package to buy is as follows:

In your city tap on one of the barrack buildings and select the 'Repair' option. This brings up the screen to repair with your wrenches/tools.

At the top will normally be a banner advertising a package to buy tools. At the moment there is a cheap package with a few tools and a very expensive package with a lot. Tap on the banner (not the buy button) to see the different options available.