I never knew there was Aurora HO scale cars, I suppose that's the equivalent of Scalextrix in the UK (now owned by Hornby and still going strong). Here in the UK when I was in my teens the only Aurora I ever saw was the AFX cars (similar to Micro Scalextric these days), I loved those and thought them way better than Scalextrix as they hugged the road better, could achieve much higher speeds and had way more detail than their bigger cousins. I even used to disassemble them, polish the armatures etc... and carefully oil the cogs and gears to make them run smoother, faster (and slower) and almost silently round the track.
Unfortunately I no longer have any of the sets as such, although I think there is some track in the loft, but I do have quite a few cars as I remember buying a whole bunch when they were on clearance in Beatties (a long disappeared model chain in the UK).
You do see the odd set appear on eBay here, but nowhere near as many as you'd have thought available...