I've happily ditched some cardboard tokens and replaced them with wooden cubes from https://railsonboards.com. In your shoes, I would buy some of their squares or rectangles (or something from a hobby or craft shop) and write my own green and red Xs on them with a market. It would also be trivial to print out some nice looking Xs and glue them on.

Just for ideas, some folks have printed their own stickers and used blank chips such as these from Amazon to make Skull and similar.