I decided to make my own valve core tool that was less likely to be lost or stolen. That turned out to be incredibly easy.
I discovered that I could make my own Schrader valve core tool in about a minute and at practically no cost. All I needed was a little section of 3/16" brake line ( which our shop always has plenty of) and a cut-off wheel to cut a small slot with.
For a good fit I chamfered a little off the diameter on the end that fits into the valve stem. It's not pretty, but it gets the job done.
Always wear safety glasses when cutting or grinding.