Finally someone that doesn't purchase out of their means.
Good job, the picture looks nice (at least on my iPhone) congrats on the new camera
Just buy new lenses. Do it right the first time. Don't cheap out. Not sure about nikon but a Canon replacement in that focal range is going to run you atleast $550-600 for the 17-40 f4L. Lenses aren't cheap either.....well atleast good ones and like I said buy good glass first. You'll save money and time. I never understood why people care about image quality when you can take 2sec to bump up the clarity in lightroom or photoshop. Well take those 2sec and multiply it times 500 or however many shots you have and it adds up quick. Same thing with colors.
Sorry for the little rant.
Not that I know of but even still they aren't selling canon anything, unless they have it instock.
Rentglass.com is one near disney. http://www.thelensdepot.com/ is another orlando based one. I'm sure you can hit up craigslist and see if there are any local ones advertising.
Lenses that usually cover most of the focal range, like the 18-200, your going to sacrifice somewhere like image quality, high aperture or just build quality in general.
If your serious about this get lenses with a constant fstop like f2.8 or lower.