These days, it's easy to get custom-made just about anything. You might want to consider what exactly you're looking for and why...
Shinai have weight and length restrictions and vary in quality. You may have one that's just for display?
At any rate, Tozando offers several options for custom made shinai from Japan. (as well as some excellent standard choices) Shipping is free and tends to be very speedy (UPS). Here's a link:
I'm sure there are others... the internet is you're oyster but deal with a reputable company.
Good Luck.
Kendo-Guide.com: Thank you for sharing! What Tozando offers looks interesting. But first we have to know how each one feels like. In many cases, we must feel it first and then we can ask shinai specialists to make our own.