http://www.garage-wiss.ch/autoelectro/autoelektro_service.htm
http://www.auto-centro.de/shop1/Komfortelektronik.html
http://www.auto-teile.com/katalog/32_marder.html
Can't see any US sites... This was a quick web-search.
In Denmark it's available in normal "IRL" shops.

Marius (Escort Cab + Mark II)