Your local Fastenal should have those and will sell them 1-2 at at time - at least mine will.
If they won't sell less than the bag/box quantity, go in, tell them what you need and why you need it - make a deal for 1-2 washers in return for them taste testing one of your beers.
Joe's Ancient Old Mead (JAOM) 10/26/2012
Apple Jack's Limeade Skeeter Pee
Skeeter Pee 10/6/2012
NB Cream Ale and AK47 Pale Mild