I just search it online and find https://www.pinholeglasses.org/ and https://www.jdharris.co.uk/pinhole-glasses offer pinhole eyeglasses. You can go and have a look. I saw it at https://www.jdharris.co.uk/pinhole-glasses that priced at $ 10.95. They are affordable. Besides, you can also search it at eBay or amazon. Maybe you can much some cheaper one there.
I recommend you to go to Amazon.com to buy pinhole eyeglasses. Amazon.com is a very famous online store around the world. It owns various of goods for people to choose. You can firstly find your satisfactory pinhole eyeglasses, and then compare the price from different seller. Finally, you can buy suitable pinhole eyeglasses with low price.