American gamelan builders used all sorts of materials including aluminum, tin cans, car hubcaps, steel, antique milk-strainers, etc.
Harrison worked with John Cage in the 40s on percussion compositions with found metal objects, resulting in alternate scaled music.
Lou Harrison and William Colvig, who met in 1967 in San Francisco, built a set of tuned percussion instruments that they called "an American gamelan" in order to differentiate it from Indonesian ensembles.
[1] These are now referred to as "Old Granddad", and Harrison wrote some pieces that can only be played on this set, including La Koro Sutro.
This inspired him and his partner William Colvig to build a gamelan modelled specifically on Udan Mas (in instrumentation, although not in tuning).