I keep getting interrupted and haven't been able to do a very complete search, and didn't find a good source for B. grandis itself, but Plant Delights nursery and Heronswood both have B. 'Heronswood Pirouette', which is on my list of 'gotta-haves'. Google will give you quite a list, mostly as far as my search went before I had to go of botanical gardens and such where you can see pictures that will make you want it more. There are several other forms too. Another source you might like to check out are the exchange forums.

Gardens North has seeds and they are easy from seed.

Here is a link that might be useful: Gardens North