Good question.  There's a Lowes store near me that has a good selection of hardware, so I think I'll check for these washers.  I bought some from Guitar Center and my complaint is that they (don't remember which brand) are a bit too soft.  It's only a concern on my snare since I tighten the heads on this drum fairly tight.  If I find a source I'll let you know.

Good tip!  Thanks Louis

If you use the nylon ones it will have a little give and the tuning rods will not loosen as easily.  At least thats the plan.  

They also make the process of tuning much smoother, especially at high tension.

Also...thanks Louis.