Rick and Moonchild,I would recommend either a Calton (rather expensive but the best and virtually indestuctible) or a Hiscox case. I use both and can fully endorse them. Both are made in the UK and both manufacturers can customize to fit the B-25 exactly. I think I have seen websites for both and will check. I know both are available in the USA through various suppliers.
All the best,
mcmoo