Hiring a building manager just to manage contractor access seems excessive. But if there’s that much work going on, maybe you need one anyway. They could also make sure tradies were working withing the permitted hours.
If your strata manager is based locally, they could feasibly run a sign-in, sign-out service for keys. I’m pretty sure they would charge you for it too.
For a less expensive option, I’m quoting from a post in a totally different thread, from Nugalbags who has solved the problem of emergency keys and other general access keys by installing a recodable security box.
we have in our block a wall mounted lock key box (https://www.bunnings.com.au/master-lock-wall-mounted-key-safe_p4210912) … only a couple Committee Members have the code. I change our code regularly as this box also holds a set door keys (for tradies), noticeboard keys, MSB keys, side gate key etc.