ICW’s rights are governed by her lease/tenancy agreement. For a start, I am assuming that ICW is a party to the lease with the landlord. If the lease is only with her housemate, then different considerations apply.
The lease would include the right to use the garage, in that the apartment has been rented out with the garage included. If ICW can’t access the garage because he/she doesn’t have a remote control, then he/she needs to demand that a remote control be provided by the landlord so they can have access to the garage.
This is presuming that the lease doesn’t provide that the tenants have the right to use the garage and they will be provided with one remote control for that purpose.
A few years ago I helped a friend of mine who had a similar problem and drafted a letter for her to the letting agent setting out that without being given means of access to the garage, the landlord was in breach of the lease. The key in that case was provided very quickly.
The same consideration applies to the gate. If your lease gives you certain rights or implies them, then not being provided with the code for the gate is a breach of the lease, in that you are not able to do something you are paying for under the tenancy agreement.
In the case of the visitors’ parking spaces, that depends on a number of factors including whether it is set out or implied in the lease, and whether the apartment that you occupy comes with the right to use those spaces. If it does, then it would be reasonable to say that you do have the right to use a space because those rights go with the apartment. The same would apply if you rented an apartment in a building that had a gym, and you needed a key to get into the gym – the landlord should supply that key.
Your avenue is with the landlord and their agent (not the strata), because that is who you have the agreement with. You need to assert the rights in that agreement and if they don’t provide them, tell them that they are in breach of the terms of the contract.