1) You are probably just getting stray voltage because there is no load connected to the port. If you want to do a quick test without an actual solenoid, you can connect an LED with a 4.7K resistor (or any resistor between 1K and 10K) in series between the COM port and any station port you want to test. The LED should light up when the station is on.
2) If you search for sprinkler valve you will find plenty of choices. For example:
I’ve mostly used Orbit inline valves (you can choose 1inch or 3/4 inch depending on your pipe size). These are also available at homedepot and lowes stores, so you can go to a store to grab one. If you need to connect these valves to garden hose, you can get NPT to GHT adapters, which are also available at stores.
Also check the ‘sprinkler valves’ section of the FAQ page to find other information: http://rayshobby.net/?page_id=207#sprinkler_valves