Good slalom spots are hard to find… That is one of the unfortunate realities…
But you’re on the right track with Industrial parks. we just checked one out over the weekend - looked very promising. butter-smooth mega-wide roads with no one around.
I’ve looked at many cycle tracks in parks sydney - so far only two have been decent for slalom. Most are too narrow, or have no hill, or too rough, etc… But keep looking, when you find a good spot you’ll know.
One thing I’ve thought of is billy-cart hills. I’ve been to one in Sydney - it was too rough but wow would be awesome if repaved. But some places have dedicated billy-cart tracks. Open up the map and start looking!
good luck spot-hunting. Looking forward to coming down in Aug-Sept to ride with you guys!