Their decision was that the people who need it must find a solution on their own
Ok, then if they have said that, then you have basically an open invitation to do what you want.
If you follow the wires from the door solenoid lock, eventually you will find that they go to a relay (either built into the Main Entry Doorstation, or a powersupply/controller box nearby). You will also, at that same point, find a 12v supply for the Intercom itself.
Take a remote control receiver, hook it up to the 12v at that point, Now your receiver has power.
Then (if it is a Strike Lock that needs power to open [and the Intercom relay is thus Normally Open], then just hook your receivers Normally Open contacts in parallel with those contacts on the builtin relay.
Of Course, if the lock is one that releases when power is removed, then hook your receivers normally closed contacts in Series with the intercom's builtin relay.
Stick a note on the receiver with your name and number, in case a technician needs to query why it is there (in future)
And there you go.
What you could even say to the Body Corp (and this might get them to be more accepting of you adding a receiver onto the system in the common property area), is tell them that you will do the above. Then program in a few remotes, and leave them with your family member (that lives there). If any other tenants then want a remote, they can purchase it directly from your family member (Maybe at cost price + a small charge for a programming fee - But that will be up to you. If you just want to charge cost on the remotes then that will be your own initiative).
But, 1 more thing to remember. If you do not go for a complex (townhouse) receiver, then if somebody looses their remote, you might have to get all the remotes back, erase the receiver, and reprogram them all.
The townhouse receiver will allow you to delete a specific remote. For that you will have to keep track of which remote is in what memory location in the receiver, and then note which owner / unit number the remote was given to.
Although you say security is not paramount, if 1 or 2 remotes go missing, if found (and if the owner has a keychain with identification details on it), then some oppertunistic shopper can just walk in the front door.