As per project specification motors with 3.7kW and above shall be provide with space heater. But vendor didn't provided the space heater for 17 kw and 4.6 kw motor... Is there any alternate solution. I'm mechanical engineer, I don't know about this.. Pls give your suggestions

Remind vendor of his obligations, and find out why he hasn't met them. You don't need a vendor who cannot meet his obligations, or an engineer who cannot do his homework, and find solutions.

Getting facts usually leads to good decisions on how to proceed and get the job done.

Wish I understood the question. What's wrong with a 4.6 kw motor, exactly?

Your supplier should remedy the situation. Short of that there are conduit box heaters which can be added. Also you can take the motors to a rewind shop and have heaters put in. Another alternative which I have not seen lately is to inject 24 volts to the motor winding when the motor is not on. Personally I would be all over my supplier to fix the problem.