To quote from the article:
“Some time in October last year, a batch of commercial compost left a Suez recycling facility in Melbourne, bound for garden centres in central Victoria and Melbourne.” …
Within days, it had been combined into soil mixes,…
"Both Suez and the Victorian Environment Protection Authority have been investigating the cluster of complaints, and have commissioned soil tests by the independent lab SESL.
Some samples have found traces of the herbicide, while others have not."
So to answer your question; it does not appear from the article that Suez on-sold to a major hardware. They did sell to gardening centres. Is that what you meant by gardening retailers?
It seems that the garden centres sold it as loose mix, not prepackaged soil.
Then, some of the claimed samples did not have detectable traces of the herbicide, some did.
I would suggest you contact the business/gardening centre you bought the soil mix from and ask where they sourced it to eliminate the possibly it may be be contaminated. If it came from Suez, you will need to contact both Suez and the Victorian Environment Protection Authority to see if they will test your soil mix.