06 Tacoma with Century Shell; Replace shell window

I bought my 06 Tacoma 5 years ago. The first thing I added was a Century shell. I bought the standard shell with a fixed front window. Now I would like to replace that with a fold down sliding window. I know that type window is a factory option, but can't find one online. Any ideas? I want to have access to the shell from my cab.

 

I did find that I can purchase a replacement sliding front window from Century, so I guess I can either go with sliding windows on my cab and the shell. or use the 4" rubber gasket boot from century.