The AC doesn't cool the house but the motor is running and I was told I need to replace the capacitor. The model# is H2rc036s06a. About how much is the cost and where can I purchase this model capacitor?

What "motor " is running. If the motor for the fan and /or air handler is running you don't need a capacitor, you may need a compressor .

The MFD rating should be stamped on the side or bottom of the capacitor and any local hvac company should have a replacement.