It may be impossible to find just the lid... but you can go to Walmart and get a kit with the same comparator block, including the lid, for < $8. Just look for a two-way test kit. And you will also get the reagents to hold you over a bit longer. The one I saw looks to be a re-branded Taylor kit.
Of course, after you procure a new lid the old one will mysteriously reappear. LOL