one option

Das klassische Problem: im deutschsprachigen Raum kennt man ein two-tier system, das aus Vorstand und Aufsichtsrat besteht. Im angloamerikanischen Raum hingegen gibt es nur das board of directors, das sowohl Vorstands- als auch Aufsichtsratfunktionen hat. Hier sollte man genau unterscheiden. Auch wenn es diese Begriffe im Englischen nicht gibt, gibt es zwei "künstliche" Begriffe für Vorstand und Aufsichtsrat: managing board und supervisory board. Viel Glück

... as well as some board members from Cologne belong to.."

is the way I read it

"a representative of GGRP and a few members of the Cologne board of directors belong to the supervisory body"
Management Board is fine (696,000 hits on Google)
although it can be used to denote a group managing something other than a company, e.g. "California Integrated Waste Management Board"
http://www.ciwmb.ca.gov/

"Local Government Management Board"
http://www.lgmb.gov.uk/

"Board of Directors" has 13,000,000 hits
and more strictly denotes the board of a company
And here are some websites of international corporations to prove it:
"Microsoft Board of Directors"
http://www.microsoft.com/presspass/bod/default.asp

GE's Board of Directors:
http://www.ge.com/en/company/companyinfo/executivebios/board...

Vorstand is not only used to denote the whole board, but also individual members

You could put "supervisory body" or "supervisory board", although the latter is strictly "Aufsichtsrat", so unless you have more context, maybe the former is safer.

--------------------------------------------------
Note added at 28 mins (2005-03-21 15:33:03 GMT)
--------------------------------------------------

More strictly to answer your query \"members of the Board of Directors\"