I studied the records available online from the Australian Virtual Herbarium and found that a possible location for this species was Skene Road in Wolffdene, a district some 40 kms south of Brisbane Airport. This fitted quite well with my route from the airport to Lamington National Park. The records dated from 1999 and stated:   Skene Road, Wolffdene. Remnant vegetation on roadside, previously was araucarian microphyll vineforest; red soil. Shrub to 5m high, prickly foliage; citrus scent to leaves. Locally common in area.
I found Skene Road and asked a bemused local resident if he had ever heard of a wild citrus in this area. He had lived there for 30 years, but didn't know of any such citrus.

I walked the length of Skene Road studying the roadside vegetation without success.

I repeated the walk, this time trying to look beyond the barbed-wire fence to the cattle-grazing fields. Although the herbarium record suggested the location was to the west of the road, access and visibility was better on the eastern side.

There was one small tree about 20 metres beyond the fence that looked a possible candidate, but it was too far away to be certain. Having got this far, I had to make sure, so I found a spot where the gap under the fence was a bit wider and rolled under the fence. Thinking back, this was probably the moment a tick decided to latch on to my shoulder - which was to cause problems later on in my trip! However, I was delighted to find that the tree was clearly Citrus australis!
This June 2014 image from GoogleEarth
GPS location: -27.773210, 153.173721
October 2016. Although I found no fruit or flowers, the distinctive leaf shape - elongated diamond to end-notched elliptical - is exactly right for this species.
Citrus australis, the Round Lime is found growing wild only in south-east Queensland. Much of the land in this region has been cleared of its original native vegetation.
page created 22Nov16

Click these links!
....finding Citrus garrawayi

....finding Citrus glauca
....finding Citrus inodora
....finding Citrus gracilis part 1
....finding Citrus australasica
Intro to Australia2016
....finding Citrus gracilis part 2
The same tree from GoogleEarth's January 2010  streetview images.