Steve,
The dimensions on yatagans tend to vary greatly. But, the workmanship on many surviving examples is tremendous. You would be better served by trying to hunt down a good example, then by trying to reproduce it. I doubt there are more than a handful of makers worldwide who can make a decent yatagan, and the price for something like that would put it well into the art/investment knife catagory ($5,000-10,000+++).
If it is just the blade shape that you are interested in, you may want to look at some mid 19th century bayonets. Virtually every Western military issued large Yatagan bladed bayonets from 1840-1880s. Some of these can be had for as little as $100.
n2s