From the outside looking in, this is a complicated problem with a simple solution. If you can raise enough signatures to call for an EGM that you may have enough support for a change to the rules governing access and egress.
If you can’t you won’t.
Depending on the size of your block, I’d recommend a mail-out of stamped addressed, pr-printed postcards that owners only need to sign and post.
Just a simple statement on the card: “I request a general meeting be held to discuss the way we gain access to parking as the current situation is potentially dangerous.”
If you don’t get enough back, you’re not going to get the votes to change anything at the general meeting.
And, by the way, if there isn’t a by-law covering access to and egress from the the car park, you shouldn’t need one to change it.