[Nyororin]

In general, most people who wear that style in Japan make their own or have their friends help them. I sew quite a bit, and I`ve never heard of a seamstress specializing in 王子 style - it`s not like it`s all that different from making like any other style.
I`m completely sure you could ask pretty much any seamstress to do it for you. It`s not like it`s wedding dress complex. You`d just have to pay for fabric and labor, like any other style of clothing.