You’re giving your own answer. A fan that’s heat resistant. You can also use a airblower that is heat resistant. You can look for a Dayton blower.
In high temp situations you need to duct the blower unit so it’s outside of the heating chamber. This way only the fan cage is subjected to the hot air rather than the motor and bearings.
Heat resistant fan is hard to get I couldnt find any , Daytona is resistant till 40celcius degree, wyowindworks ducts maybe good idea.
airblower is to weak for my oven - 1,5meter x 1m x 2m
Look better and you find a lot more dayton high temp blowers that will fitt your oven.