I would start with the ABS gov web site...who do various reports....gain their information from businesses on a regular basis (confidential)..you might also check out same site for CPI figures...as most commercial ents are tied to the CPI....and the capital city for each state....for eg in NSW we use the CPI all groups Sydney, and in Vic the Melbourne all groups CPI....another source might be the shopping centre owners...look in their annual reports...for eg; asx code GPT
most prefer to keep lease information confidential....
the realcommercial web site which lists commercial properties...may help, you can check out what the lease figures are if disclosed....
I checked that site this morning for friend looking to lease retail premises....the regional city we looked at had only 2 retail properties available..but plenty of industrial and warehouses....
the RBA govt web site is another that produces information....
they are the sites I base some of my research on , when deciding the lease renewal figures.....
look at other commercial real estate agents.....Colliers springs to mind, and they do have some good reports on a regular basis...