Fc 28-22 problem

Hello all. I am new in multirotors so i have a big problem i have fc 28-22 motors and it happened 2 time that a motor went out because one of that 2 screws was unscrewed i think because of the vibration. Can you help me please with some information any suggestion would be great.
PS: another information what can be great i have 4 motors fc 28-22 with bended axis and i cannot find spare parts to can use them again. I damaged them in my first flights

You must ensure against vibration in all your fixings.

Threadlock on the motor screws is very good idea to stop the screws coming loose.
There are different grades but a medium is probably best as it will allow you to get the screw out if you need to.

Part of the learning curve in the DIY building is not just cheap components but also spare parts.
Check the motor shaft size as most are a standard 2mm or so.
Have you checked where you bought the motors from?
Have you checked your local Hobby Shop?
Have you tried puling the bent shafts from the motors?