A number of years ago when I was working on projects at the German division of a Canadian sterilizer firm, I was introduced to a firm called MeCu who carried a wide range of brass (messing) and copper as well as lots of other metall-stucke.
Here's a link to their website's spec page for various round brass tube.
https://www.mecu.de/images/mecu/mecu_homepage-tabellen_messing_Rundrohr.pdf
Maybe they can help with your requirements. Not sure if they are OK with working with individuals, but years ago, company to company, with business conducted in German, they were very responsive and helpful. Good luck!
Edited By Jeff Dayman on 19/09/2018 22:22:54