I'll have to admit, the only chocolate I have found in my grocery store, does not come in large quantities and certainly is not reasonably priced. That said, I usually use Guittard chocolate and I get it at the Colorado Nut Company in Denver.
Please keep in mind that tempering chocolate is time consuming and challenging at first, so you will want to practice as much as possible before you have to do it for real.
What you will need:
At least one pound of Chocolate. The only fat it should contain is cocoa butter.
pot of hot water,
bowl, I prefer to use a stoneware bowl
good digital thermometer
1. melt your chocolate gently!!! Do not overheat chocolate. Try to keep the temperature around 106-110 F. Never over 110 F. I generally melt my chocolate in microwave in 1 minute intervals.
2. once melted stir gently off heat until the temperature is around 95 F. Add a few pieces of chocolate that are already tempered. It will help your melted chocolate start to form the proper Beta crystals,
3. Once the added chocolate is pretty much melted, paint with your finger, a streak of the chocolate on the parchment paper. Note the temperature and continue stirring chocolate. For every degree the temperature falls, make additional streaks of chocolate on parchment, also noting the temperature. The chocolate should dry within a minute or thereabouts, and should be shiny. I generally find that the Guittard dark chocolate tempers at 92 ish F.
4. Once you find the temperature in which your chocolate tempers, you will want to maintain it at closely as possible. If it starts to cool to put your bowl on top of the pot of hot water to increase the temperature slowly.
4. If the temperature falls too low, for me below 88 F, you will have to start the whole process over. However, since the chocolate is already melted, you can usually heat it to 96 F and that will shorten the process a little.
A well tempered chocolate should be shiny, have a nice snap and a smooth feel in your mouth.
Dark chocolate is much easier to temper than milk chocolate or white chocolate, which isn't technically chocolate.
Hope that helps. Good luck