I hate the internet. No really, you all suck. I ask Google where to find 10mm ID (well, 10.3mm, to be exact) copper crush washers locally, and I get back a million hits leading to forums where dozens of people are asking the exact same question, with a lot of "uh, I dunno, it was at my local [insert auto parts store here], the guy behind the counter found them for me". Why would you want them? Most Mitsubishi brake line banjo fittings require them, as do Mitsu and Subaru turbo oil feed banjo fittings.
The answer is NAPA, and the part number is UP 24951: "Washer - Sealing", in their brake parts lineup. To the next guy on the Internet searching for them, there you go. :)