Agree with
kappykaplan...........they will measure, fabricate one to custom fit to your specifications (length and height) and install. If you want to buy one on line like
Bimini Tops | Overton's (overtons.com), you will need to task measurements (width for mounting on the gunnels and height) and install it yourself. OR you can fabricate one yourself from aluminum or stainless steel tubing per this link
How to Make a 2-Bow Bimini Top (sailrite.com) . All you need to do is measure the width for the mounting locations, then buy the hardware (bows, mounts, etc), and canvas and get the the tools. Next you assemble the hardware on a sheet of plywood at home, sewe the canvas and fit it all up from there. Another option is to go to the Sailrite website
DIY Bimini Kits, Make Your Own Bimini (sailrite.com) and they give awesome instructions on how to build your own. Make sure you get Sunbrella to resist fading.