Jo-Ann’s Fabrics is offering free take-home-to-sew face mask kits. The PA store has kits of materials to sew 5 face masks (limit one kit per person at a time). Return the completed masks to the store.
Also, you can use elastic from other products, such as head bands, hair ties etc., which should be available at many stores.
Here’s a more complex mask that includes a pocket for filter material:
Background info & discussion on this mask