Some may prefer not to answer as this is dismaying to many. If the gray plastic is secured by a ring that has been crimped to leave two ‘ears’ that appear on either side of the ring, then the tubing is probably polybutylene. this material has been accused of being inadequate for the service.
Much of the debate was begun by inadequate or improper rings that hold the tubing to the fitting; the proper pressure must be applied to hold the tubing to the fitting. There is a special tool to do this. Installation without the properly adjusted tool on the correct rings can produce potentiality for releasing the tubing from the fitting with resulting water damage.
I have this tubing and fittings connecting my water heater to my domestic water lines for 20 years now without a problem. I am sure you have little interest in changing all your tubing to PEX (or copper) which does not have the problem at this moment.
So to find someone to provide fittings for this purpose is not the only problem. You must have the correct tool to do the job. If you find a plumber willing to do this task; I recommend that over buying the tool yourself.
Others here may give you additional information about remedies; they have done so in numerous answers that you can find by going to the bottom to progress through prior libraries of answers relating to plastic pipe.