How long an arm do you want?

Does it have to be an original part?

I will be using telescoping stainless steel arms such as ones you can find on eBay by searching: stainless steel bracket mirror

Here are other possibilities:

http://www.grote.com/product.php?product_number=10002

http://www.grote.com/product.php?product_number=10025

http://www.bigrigchromeshop.com/Merchant2/merchant.mvc?page=BRCS/PROD/UEMB/UP60021P