Local (savings) banks (e.g., the savings bank in a county, Commerzbank, BNP Parisbas, Volksbank, DekaBank, etc.) often have foundations that fund projects, events, exhibitions, etc. in the art and cultural sectors or that offer sponsoring. Such grants often require local relevance of the funded project. Research and inquiries can pay off.
Local companies often have an interest in acting as sponsors of local or (supra)regional projects. Larger companies post information about this on their websites. Simply write to or call smaller companies.
Partnership programs between cities and municipalities exist in many places. They are interesting contacts for international projects.
Art in architecture has a long tradition in Germany that goes back to the Weimar Republic. Since the recommendation of the German Bundestag in 1950 to use a fixed percentage of the construction costs of all federal buildings for art, numerous works of art have been created on behalf of the federal government for buildings at home and abroad. The contracts are often awarded through international tenders. Information is available from the Bundesamt für Bauwesen und Raumordnung (English: Federal Office for Building and Regional Planning).