Help replacing cooktop

Help! The electric cooktop on our kitchen island has a broken glass top (it's a Jenn-Air, with a down vent in the center). We'd like to replace it since it is pretty old. However, the opening is exactly 21-1/8 x 28-5/8", and every one of the 30" cooktops I find on the Internet requires 28-7/8".
Any idea where I can get a 30" down-draft cooktop that's just a little smaller than the rest?
Otherwise I guess I have to cut through tile, Wonderboard & wood to enlarge the opening.
Thanks,
--Doug
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it's pretty easy to cut the countertop using a handheld 4" wet diamond saw. makita makes one. ask at a rental shop what they have that could cut it.
if you don't mind an absolute mess, you could cut the tile/wonderboard with a masonry blade in a circular saw, then a plywood blade for the underlayment. remember, only the top has to look pretty, and a lot of that will be covered by the stove flange.
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enlarge
Harbor Freight for diamond bits. I have an assortment from 4-10 inch. None are very expensive and since I only use them occasionally they last a long time. I even used one in my cordless saw because I was concerned that the big saw would get away from me. Took a little bit longer, got the job done. I have found time is only relative to the finished product. Perfect is acceptable.
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