Hmm, I used to GM SR3 a lot but never did anything with Berlin.
If I were in your situation, I would prepare some amazing German food for the session. Curry wursts and other sausages, braised red cabbage salad, German potato salad, and some good dunkel beer. You can then run something very generic filled with comical stereotypical characters that is mostly a combination of tactical challenges with a bunch of jokes, and everyone will have had a great time. That way you won't really need to know too much about what it had said in old sourcebooks of yore.
EDIT: Maybe the runners can be hired to retrieve JFK's Berliner doughnut which holds his soul. The doughnut is guarded by a cabal of Teutonic sorcerers who want to create some kind of magical neo-Germanic empire in which everyone will be forced to be a vegetarian. They need to find their savior ubsermensch figure whom, they have prophecied, will gain world-destroying power once he eats the JFK Berliner doughnut. During the quest, the player characters find a unique relic; JFK's M16A1. This is the one and only magical firearm in the SR universe and it should not be able to exist according to the setting. Somehow, it has been maintained using magical gun oil that summons the fighting spirit of JFK and allows the wielder to add dice to ranged attacks made using this weapon and in this regard behaves like a weapon focus. (Make the power of the focus something such that a character would be able to bond with it during the course of the campaign). However, in spite of this tremendous power, every time the rifle is fired, roll 1d6. On a roll of 1 the rifle experiences a type III stoppage that requires 3 consecutive Complex Actions and a Rifles (B/R) skill check (TN6) to clear. If the skill check fails another 3 Complex Actions are needed followed by another successful skill check. Even if the skill check succeeds, the user must strip the magazine so the rifle must now be reloaded before it can be fired again, plus one cartridge per skill check is lost, dumped on the ground. The weapon is drawn to the 'runners to help them rescue the jelly doughnut from the Teutonic sorcerers and once the goal is accomplished it magically disappears from the world until the next time it is needed. (And then maybe refund the karmic bonding cost. Either that or let the rifle stay, maybe make it an NPC; let it have JFK's personality and only want to work with 'runners who support JFK's ideals. Depending on the party maybe the JFK rifle can become SR-ized intelligent weapon in the tradition of D&D; if the characters are too evil the rifle somehow escapes into the world to help idealists fight corporate tyranny or something and becomes a recurring character.)
Here is a picture of JFK's rifle:
http://www.the-puzzle-palace.com/JFK-M16.gif