You're not 'entitled' to know her address, per se, but if you end up filing for Court, that information is going to come to light one way or another, be it through a location order so you can serve documents on her, or a parenting order that both of you must tell each other your respective addresses.
Note, here, that the best way to find out where your son is living is by requesting a location order from the Court, which will force government agencies to disclose the last known address of your ex so that she can be served with the Court application. This is usually made early in proceedings because they can't proceed unless the ex has been served, but you should try a process server first. No matter what happens, though, she's eventually going to need to disclose her address, either to you or the Court, as well.
What you should know at all times is that your son is safe and well, which is obviously the role of the police in carrying out a welfare check. I hope you responded to her barrage just once and said something to the effect of 'I requested a welfare check on X because I don't know where he is, nor if he is safe. If you wish to assist me with this problem, I'd be more than happy to negotiate a care arrangement for X that ensures this information can be shared without needing police involvement. I look forward to hearing from you to again in the near future to discuss X's care arrangements and negotiate an agreement.'
Note, here, that the best way to find out where your son is living is by requesting a location order from the Court, which will force government agencies to disclose the last known address of your ex so that she can be served with the Court application. This is usually made early in proceedings because they can't proceed unless the ex has been served, but you should try a process server first. No matter what happens, though, she's eventually going to need to disclose her address, either to you or the Court, as well.
What you should know at all times is that your son is safe and well, which is obviously the role of the police in carrying out a welfare check. I hope you responded to her barrage just once and said something to the effect of 'I requested a welfare check on X because I don't know where he is, nor if he is safe. If you wish to assist me with this problem, I'd be more than happy to negotiate a care arrangement for X that ensures this information can be shared without needing police involvement. I look forward to hearing from you to again in the near future to discuss X's care arrangements and negotiate an agreement.'