For the boxes, check out candy supplies. Like the ones for weddings and events. Also, bead and jewelry supplies. I typed in "Small acrylic box" on Etsy and got some shops. For the larger display cases, AC Moore used to carry box frames that were acrylic. They don't have them anymore but the art supply store, d*** Blick has them on their website and they aren't too expensive. You would just have to cut one more acrylic piece for the back. I am using one right now for a shop window and it is working very nicely. They come in different depths too.
link to the frames: https: