I went to a Yamaha dealer, Auto Zone, Ace hardware and a Moto Guzzi dealer. None had aluminum or copper crush washers. Finally, at AAP they had crush washers for brake lines that were the right size. $2.99 for 2. Copper must be a precious metal.
BTW, Auto Zone has Castrol MC oil and Valvoline MC oil $2. off. Comes out to $1.99 a quart. I bought some for the Enfield (The Ural uses Yak oil).