You can buy it online at the Eurail website as Mobilepass for your phone. If you want a paper version of the pass you can buy it from DB Ticket offices “DB Reisezentrum” at major stations. 

DB say in their terms and conditions they sell paper Eurail passes at these stations:

Berlin Hbf, Berlin Flughafen BER, Dresden Hbf, Düsseldorf Hbf, Frankfurt(M) Hbf, Frankfurt (M) Flughafen, Hamburg Hbf, Hannover Hbf, Heidelberg Hbf, Köln Hbf, Leipzig Hbf, München Hbf, München Flughafen, Stuttgart Hbf.

Hint: check first by yourself If AZ is indeed to buy EUrail-the former ex CCCP and often still Russky angehaucht Nations were told to use INTERRail-that may pose problems for you if you stay longer in DE as then the home-country rule is in force. There is NO pass that lasts for 6 monthes. And maybe/perhaps, if its mainly for doing some weekendtrips out of DE then a reduced bahnCard and booking advance Sparpreistix may work out better/cheaper.

BUt IF you can: then by now only DE and CH (and maybe perhaps AT) are the only countries left where one can buy a paper EUrail right on the spot in a very few major stations/airports.

@mcadv Please don't write confusing information. Azerbaijan is an own country and not seen as a part of Europe, thus persons from Azerbaijan can buy a Eurail pass. 

Everyone who can't buy an Interrail pass should buy a Eurail pass. 

Please check yourself before you confuse others. It's all on the Eurail website. If you can't bother to check, then please refrain from replying.

You know that this is incorrect, so please don't write such nonsense.