Jim,
I searched for birch crotch veneer several years ago and couldn't find any. Someone suggested that I try avodire (African satinwood). It is similar in color but most of the avodire flame that I've seen is not as intense as birch. I finally did find what I was looking for--a flitch of tightly-figured avodire crotch--on eBay. Ask your veneer supplier for a reasonable substitute.
Mark