Finy, The friends I stayed with in WA for a week, drove me to Kings Park. The wild flowers there was lovely. Then they drove me up the coast, as far as York I think it was. It was a very small town, with hardly any people around. It used to be a monastery. I think I was there back in the late '90's. We saw so many wildflowers!
Never on a guided tour but my husband and I regularly go driving and hiking in the Hills and beyond during spring, hoping to spot some wildflowers. Some of the nature reserves on the Wheatbelt are good places to head for.