When I cut the blank for my William Antes pistol project, the board I had was large enough to cut it at a slight angle for better grain thru the grip. It did make it really fun inletting the barrel though. Here is a photo.
The piece above the pistol is the slab I cut off of the side of the blank. You can see how the grain runs thru it.
Here is a blank that I have for my next pistol project, an 1805 Harpers Ferry pistol. The grain runs about perfect in this blank, but as Mike said, they can be hard to come by.
I'm like you, I would prefer the grain to not be parallel to the barrel, but I don't know if you will have that choice or not when buying a blank.
Mark