There is a well-known formula for these structure constants using character theory. It has a slightly different form to the one you write down (which doesn't look right to me), and you can find it as Exercise (3.9) of Isaacs' Character Theory of Finite Groups.

You can find an electronic version of this book here. For the record, it's one of my favourite maths books ever.

There is a well-known formula for these structure constants using character theory. It has a slightly different form to the one you write down (which doesn't look right to me), and you can find it as Exercise (3.9) of Isaacs' Character Theory of Finite Groups.

I have an e-version of this book so, if you want a copy, email me. For the record, it's one of my favourite maths books ever.