Your best bet would be to look in the local German Gelbe Seiten
(Yellow Pages) look under auto and folie or "Lack Schutz Folie"
http://www.gelbeseiten.de/yp/quick.yp
I found these three results for your search. I have no idea IF they are any good. You could also stop and ask any Taxi driver where they had thier Taxi covered. Most of the Beige Taxi's have foil wraps on them!
Heidelberger Lackfabrik Rentzsch GmbH & Co.
Kurpfalzring 100A, 69123 Heidelberg
Tel: (06221) 74 85-0
Branche: Farben und Lacke
In Karte zeigen In Merkzettel übernehmen
Tinti GmbH & Co.KG
Mittelgewannweg 10, 69123 Heidelberg
Tel: (06221) 7 51 11 00
Fax: (06221) 7 51 11 17
Branche: Farben und Lacke
In Karte zeigen In Merkzettel übernehmen
Schlechter B.
Dossenheimer Landstr. 103, 69121 Heidelberg
Tel: (06221) 47 33 43
Fax: (06221) 41 91 93
I found my "wrap guy" quite by accident... I saw this Audi A6 wrapped in a flat black color... and then noticed his ad for his advertisement services. He was local to me, in Coburg. I think that is too far from you. I can PM you with his number IF you like>?
You can also try looking under "werbung" for advertising in the yellow pages too.