You are best off getting your local store to fit for you, reason being that they SHOULD re-tension the entire wheel when fitting, very important if you don't want to end up with more broken spokes. Please note the optimistic use of the word, 'should'
Also the right side is slightly shorter than the left to allow for the dish of the wheel, and the length will depend on how many spokes you have. If you are going to have a crack yourself make sure you measure the correct side! I will only build with DT Swiss double butted spokes, and all good bike shops should have access to them via Madison.
I did used to know the spoke lengths off the top of my head but with so many pin codes and security numbers logged in my head 'tis but a distant memory.....
I hope that is of some help.