Hi,
Min 2.4m is the current code requirement for parking width and has been in place since 2003. The Australian standards in the format we currently know them was only formalised in the mid to late 80’s, so you wont find an earlier version of AS2890 than 1986. I cant even tell you what it was (if there even was one). You might be able to find old hardcopies in the State Library. You’ll find nothing online. Is there physically any space to increase the size of the parks? Are what your asking (wider parking bay) not physically possible? If so then I’m afraid it might be a case of buyer beware as the current parking space meets current minimum requirements.