Like most things, Google is your friend. Try searching for laboratory supplies or science supplies. l live in Canada and many retail shopping malls have science stores that sell to budding young experimenters in all branches of science. They sell all the common chemistry lab glass ware at high prices (Test tubes $1.25/each compared to a few cents if you order of the net in quantity). For the number I used and broke it was just more convenient to buy from them than to order off the net.
If you are using plans from Jan Ridder or other European designers, be aware that some of the test tubes they use are not available in North America. One builder on this board overcame that by buying Pyrex tubing in the proper id and then plugging one end after cutting to length. I took a different approach and mounted a standard test tube to an aluminum cylinder instead of using the test tube as the cylinder.
