These are not test tubes but powder tubes, made of plastic so they will not break or when they, in the very unlikely case, will explode they will not send glass flying around.
Have had some that cracked at the top when the cap was put on, but this guy sells good quality.
I live in Holland but bought these on the internet from a German blackpower parts dealer 'Stifters gun Flints'
I am not sure he ships to the US, probably does though since he ships to Holland as well.
Not sure what shipping would be.
http://www.stifters-gunflints.de/
The Index page of his site, go to 'SHOP' and you will see all kinds of articles on the left of the page.
The power tubes are called pulverrorchen in German
The partnumber for the 50 grain (20 in a box like on the photo) is SER50 (5.00 euro)
SER75 is the same for 75 grain tubes (5.50 euro)
SER100 is the same for 100 grain tubes (8.50 euro)
The tubes only are availabe too:
PR50 = 50 grain tubes. 100 for 12 euro
PR75 = 75 grain tubes. 100 for 14 euro
PR100 = 100 grain tubes. 100 for 18 euro
Hildo