Sometimes it's not necessary to know the exact CG specified by the manufacturer. You're going to want to tweak it anyway to find the best balance for your type of flying. A good starting point is about 1/3 of the way back from the leading edge of the wing at the fuselage. If you have dual rates, set a high rate for elevator that is about 1/4 to 3/8 inch greater throw up and down than your low rate so you don't run out of elevator on landing if the plane is too nose heavy. You can also use try using 50% or more minus expo on the elevator instead of dual rates. If you're running a pumped engine or a YS, the fuel tank CG is best located right on the airplane CG or about 1/2 inch behind.

If you plan to fly patterns, try NSRCA.org and print out the trimming chart. Better yet, find someonw else who's doing the same thing and team up. The trimming chart will tell you how to trim, but someone who understands pattern can tell you why things happen the way they do.

Good Luck