I make my own. I start with black construction paper. Paint it an appropriate color (Grey primer, Red primer, Flat Green, Any of the above in one hand and flat white in the other, etc.)
For 3-tab, I cut strips and notch them with a knife, using a plastic square notch flooring adhesive trowel as a guide.
I also use pinking shears and various similar craft scissors (or even a cow-shaped paper punch) to make other shapes of shingles.
Glue them down with Elmers.