Here is a another source for fire steel tubes. I am not associated with either of the companies. These steels are mischmetal.

firesteel.com has sizes from 3/16 to 3/8. The 1/2 steel is no longer available. I was able to chat with Ron and said he had one left which he sold to me. Not very practicable for a PSK because of size and weight so this for my small collection of fire making tools and not my PSK. Pictures and report to follow once I receive it.

https://firesteel.com/categories/FireSteel-Tubes/

goinggear.com sells the mischmetal steels in the raw. Roll your own with 1/2 x 12" mother of all fire steels! Does any know of a source for these aluminum tubes (or similar)?

http://goinggear.com/index.php?main_page=index&cPath=4