Try
www.emsduc.com they sell shim kits as well as individual shims as well as tools and DIY books. You'll need the closer shim measuring tool either way, 'primo will charge you a half hour of labor to measure the shims for you. The $10 tool pays for itself in one valve change considering $60 hourly rates (at the low end).
The shims at EMSDUC are $9.50 per I think, which is comparable to the trade in rates at the local places (probably cheaper). You have to wait a few days, but you get to keep your old shims, which in the long run might work out. Just store them in a plastic baggie or something after coating them with a bit of oil.