I doubt you'd get an off the shelf cover to meet your needs. It will have to be something bespoke. Unless you DIY, it'll be very expensive.
One other thing - although our boat had a proper camper cover, it'd be virtually impossible to keep it up whilst on the move. Where the clear PVC section is rolled/folded up, it distorts your vision too much. It's be like trying to drive the boat looking through bathroom window type frosted glass! I'm sure it's not a problem on the bigger boats with taller windscreens, where you can still see through he windscreen.
That said, you can get off the shelf biminis that would probably fit. In fact, I found this picture of one on a 17' Fletcher:

With a bit of modification of the bimini part (addition of bungee toggles and/or press studs) this may provide a good basis to make a 'front' and 'sides' that would attach to produce a sort of camper cover. It wouldn't be perfect, but should be functional and would be cheaper than having a pro job done. You could try and do a pro -standard job yourself (proper covered zips and darts all over the place to get around all the 3D corners), but prepare to tear your hair out! I know my way around a sewing machine really well, and decent marine canvas (e.g. Sunbrella) works really nicely on any half decent sewing machine, but the sheer size/bulk of material that you have to handle whilst sewing makes it really hard. I ended up modifying our dining table so that I could integrate my machine into it to make a really large machine table. Even then, it wasn't easy.
One other thought, as well, if you would only use the front and side bits when the weather was a bit off, then you may be able to get away with PU coated nylon (not UV stable) which is SO much cheaper than proper, marine grade, UV stable acrylic canvas like sunbrella (£20/meter). This way, any mistakes you make will be a bit more bearable!