I've picked up several at thrift stores. With names like Holly Hobby, they were sold for children. My brother is a carpenter and made one for me to my specs, 2' X 2' X 6" deep at the shallow end and 8" at the deepest. The slant from 8" to 6" makes it more comfortable to lean over. Instead of glass, I had a piece of plexiglass cut to fit inside on a small lip. The only problem is that my husband put a light in it for me and it will roast you. I don't use it nearly as much as I thought I would, partly because of the heat from the light. Lowering the light and changing to something like leds will be the next Honey-do I take to him.
If you were satisfied with tracing on a window, you might be happy with using some of the make-dos used before we had so many toys.
1. A dining table pulled apart, table lamp placed underneath on the floor, and a piece of glass placed over the gap where a leaf would have been.
2. Two stacks of books on a table or counter, enough space between stacks to place a small lamp or light source, and a pane of glass above the light and resting on the books. The hardware store will usually cut the glass or plexiglas to any size you want.