Apollo Microwave convection oven issue

You can get away with replacing it with a microwave from Walmart or such. But not so sure about a microwave/convection. The Apollo has an exhaust fan to blow the hot convection oven air out the front so as not to overheat the inside of the cabinet. Or at least our does. You would need something similar with another brand.
Ours, in our '07 Montana, also quit several years ago. But at that time they were easy to get replacements or parts.
Did you try this site?
I got mine from Midwest Sales.