The big West Coast mirrors are available new from your local NAPA or big truck parts house. Most new sets have adjustable arms. Amazon and eBay also have lots to choose from...
Click on Mike's Garage below my signature and see my '56 8400 tow truck and '56 LCF...they both have different types of mirrors that I believe are original to each truck. The Fire Engine has original single arm mirrors.
Hope this helps,
Mike B
