I recently discovered an outdoor sculpture that includes a trombone and included it in the Trombone History Timeline (20th century). See 1979, below; special thanks to Berthold Huss. The other outdoor trombone sculpture that comes to mind is also from Germany (see 1989, below).
1979—Quedlinburg, Saxony-Anhalt, Germany: Wolfgang Dreysse includes a trombonist among the 4 musicians in his bronze sculpture, “Münzenberger Musikanten.” This monument to Münzenberg musicians, many of whom made their living playing music for various occasions, is located in the town’s market square (see below image; used by permission of Berthold Huss).
1989—Soest, Germany: Sculptor Kord Winter fashions a trio of musicians in honor of one of the city’s most famous residents, 16th century artist Heinrich Aldegrever. The sculpture makes reference to Aldegrever’s Die Posaunisten from the series The Great Wedding Dances of 1538 (see 16th century timeline) (see below image; public domain) (source: wikimedia commons; see also www.kordwinter.de/objekte/Brunnen/brunnen.html).