First, grade 20MnV6 does not appear in DIN EN 10297-1.  It is probably most commonly specified for hollow bar according to ISO 2938 or similar, but some European tube manufacturers offer this grade as a high strength product.  Second, you can find the nominal composition from any number of websites:

http://www.google.com/search?hl=en&lr=&as_qdr=all&;q=20MnV6+filetype%3Apdf&btnG=Search

Third, there is no exact equivalent of this grade in ASTM A 519, which is the seamless tube standard in North America that most closely resembles DIN EN 10297-1.  North American producers of seamless steel tubes, such as Plymouth Steel or the Shelby facility of ArcelorMittal would likely produce 20MnV6 if you need large quantities.  What size tubes do you need?  Quantities?