The answer is to make your own of the other type, either from acetate or card, the choice is yours.
Here is how it is done in Studio - so easy and you can vary the shape, size and colour!
The 'subtract' is under the modify page, as is the weld.
For some reason, you need to fill the basic shape with colour for these steps to work, I tried it without and the results were different when I tried to modify it. The key shape is left unfilled.
You can make a lot from just one sheet. Larger versions could be used at parties for putting on glass stems as identifiers.