Richard has the best solution ( unless you have experience cutting out and inlaying ivory)
If you have about 20 keys.
Using 14 keys, laminate up a block of ivory and colored fiber spacer material. Black would be my choice, but whatever you like will work. Make it about 1" wide. Epoxy it up with good quality resin,and let it cure in the clamps for 24 hours. Only clamp tight enough to hold snug, or you will squeeze out all the epoxy. Cut this in half and use it as bolster blocks. If doing scales, you can use these as a striped bolsters with the stripes running vertical.
If doing a hidden tang, you can make a fancy block. Continue on by sanding one of the striped sides of each laminate block flat, and epoxy the block together with a strips of spacer material and ivory pieces between the joint. This is a bit hard to describe, but since one ivory piece isn't as wide as your blocks are, you will use two pieces in each laminate ( side by side - sticking out a bit on each side of the block). This won't show, since the joint will be down the center of the block ( and drilled out when the block is fitted to the tang). Use four pieces of spacer material and six pieces of ivory. Place these between the two blocks (S-I/I-S-I/I-S-I/I-S). This new lamination will be at 90 degrees to the laminations in the blocks. Sand the block down to remove the excess ivory sticking out, and you now will have an approx. 1+" wide by 1.25"+ by 1.25"+ bolster block. This will make a neat looking block. Install it with this last lamination running horizontal ( ricasso to butt axis) on each side. When you grind the block ( avoid heat buildup ,or you will scorch the ivory) the laminates will look like fancy diamondwood.
