Thanks to a fellow member of englandfans, I've been pointed in the direction of this German forum (http://forum.tooor.de) that has a lively and popular World Cup ticket exchange section. 

Like all such Internet exchanges, the same need for caution applies ... but as you're swapping here and not buying and selling, there seems little scope for touts to get involved.  However, beware of fakes and I would recommend a face-to-face swap at a FIFA ticket centre, so that you can both do a name transfer.

How to register
If you've registered for a number of English forums, this process will be familiar to you - only in a different language:

1. Click Registrieren in the top right-hand corner
2. Accept the forum rules by checking the box next to "Ich habe..." and clicking Registrieren.
3. Enter a user name in the Benutzername field.
4. Enter a password in the Kennwort field, and repeat this in the second 'Kennwort' field.
5. Enter a valid e-mail address and repeat this.
6. Type in the security code displayed.
7. Ignore the remaining fields and click Registrierung abschicken (Submit registration).

Completing registration
You will now receive an e-mail entitled: Noch ein Schritt zur ....  Click on the first link in this mail to activate your account.  If using AOL, click on the second link instead.  Your account has now been activated and you can log in (Anmelden).

The swap forum
Once you've logged in, scroll down to the forum called Tausch (Swap).  To help you read the German posts, here are a few tips:

Suche = I'm looking for
Biete = I'm offering
Tausche ... gegen ... = Looking to swap ... for ...
AF or 1/8 = Achtelfinale = Round of 16
VF or 1/4 = Viertelfinale = Quarter-final
HF or 1/2 = Halbfinale = Semi-final

I suggest you reply (Antworten) in English.  If you want to submit a new post, click Neues Thema.  It may help to put the heading in German at least, e.g. "Suche 1x AF Stuttgart, biete 1x VF Berlin" (Looking for 1 round of 16 in Stuttgart, offering 1 x q-final in Berlin).  Then do the main post in English.

Private messages
There are several settings you can set in respect of PMs (in German Private Nachrichten or PN for short).  Once logged in, click Kontrollzentrum (Control centre) at the top of the screen (towards the right).  In the control centre, click Einstellungen ändern (Change settings).  In the box entitled E-Mails, Private Nachrichten und Benachrichtigungen the check boxes are for the following:

1st box: Administrators may send me e-mails
2nd box: Other users may send me e-mails
3rd box: Activate private messages (is checked as default)
4th box: I would like to be notified by e-mail of each new PM
5th box: If I am logged in when a new PM is received, notify with pop-up

If you get stuck, e-mail me at info@theworldcupingermany.com and I'll try to get back to you ASAP.

Hope you find the tickets you're after!

PS - Please note the rules of this forum are swaps only - no selling!