Both KitchenAid & Jennair make a 36 in. downdraft gas cooktop still. Have you tried to find a granite fabricator who will enlarge your opening to fit a slightly longer cooktop?

https://www.bestbuy.com/site/kitchenaid-36-gas-cooktop-stainless-steel/5771907.p?skuId=5771907&ref=212&loc=1&extStoreId=886&ref=212&loc=1&gclid=Cj0KCQjw5ZSWBhCVARIsALERCvyB_uEDP3E7HehgRcRfd56mKMNyVjb0PydcWcTKSMmZjkrPJk6jvwAaAhOHEALw_wcB&gclsrc=aw.ds

The kitchen is in the center of house so there is no outside wall to vent though. We have tried talking to several granite companies and none are willing do more than replace the whole countertop. They just don't want to deal with what they consider small projects.

i wish you luck! i had a similar situation of having an older cooktop being an odd size. they make trim kits to fill in the gap from the old to new size. and this will depend on the depth of your counter but also look into a telescoping downdraft and then i would go with an induction cooktop because these have the least amount of particulates and pollution thrown out into the kitchen vs gas. i prefer it over gas and glad i made the change. when i needed a new cooktop i worked with through a local family owned appliance store, not the countertop company, so try one of them? they were also going to do the cutting counters etc. but i needed the trim kit instead with the cooktop i chose.

Is it possible to find acooktop that will leave room for a telescope downdraft?

The Kitchenaid KCGD506G and Jenn-Air JGD3536G are identical. You need to measure the size of the existing, granite cutout to see if the replacement would fit in it and then check the dimensions of the parts that hang below the cooktop to see if you have space for them, and that the gas pipe and electrical outlet are in acceptable locations. You can see that the locations of the downdraft vents are different than that of your old cooktop so some rejiggering of the ductwork below the cooktop would probably be necessary.

"They just don't want to deal with what they consider small projects.:

No, they're too afraid to tell you that they'll do it for $750.00.

Building on Joseph Corlett's comment--have you tried asking them if there is a price that would make them take the job? They might be underestimating the price you are willing to pay to solve this problem.

This is a 36" induction cooktop from Ikea. Electrolux makes it.. 5 year warranty. You'll need a 220v 40 or 50A circuit. Bosch and Miele also make units. Best Cattura makes the preferred telescoping downdraft vent.

Buy the same model used on Ebay. Is this the model? There are several on Ebay. Definitely a market for it....they are selling for $700-$800. But might be the cheapest option if you can get 5 more years out of it. Click to be directed to Ebay website ----- Jenn-Air Expressions Black Gas Downdraft 34 inch Cooktop/Stovetop CVGX2423B

this one looks nicer and will ship

click here

Here's the installation manual for your JennAir Expressions gas cooktop.

https://www.manualslib.com/manual/637588/Jenn-Air-Cvgx2423b18.html

Looks like a KitchenAid 36 inch induction cooktop would fit in your cut out dimensions, no downdraft vent, though. Maybe you could live with a recirculating vent overhead, if you can install one. Surely they are better than nothing?

I switched to induction, and it doesn't throw out as much heat or splatter. A boiling pot still produces a lot of steam, of course, but my wimpy vent and the kitchen ceiling fan make the area quite comfortable. I'm so glad I didn't ditch the ugly ceiling fan for style's sake.

Thank you all for the suggestions and helpful links!