Boxy looking plastic lids are available, and are better than nothing:
As you found out, replacement lids are pricey, if available at all. Most manufacturers do not stock lids for toilets which are no longer in production. And that Home Depot Tijuana Special, the Lamosa, there were never any spare parts available. Generic parts work inside, though.
It is not a quality toilet at all, and a new one would be under $75, complete, so I would not spend any money on a lid.
I should add that if it is cleanly broken in just 2 pieces, many people successfully glue those together with some 5-minute epoxy. Get a clear, or white, glue. This will be sturdy enough, and if you put a doily or a plant on top, no one will notice the glue line.