Over the past 10 years or so there have been a number of discus breeder/importer suppliers in the GTA/Toronto/southern Ontario area, but none have seemingly achieved any consistent degree of success and all that I was aware of have apparently disappeared for lack of viability.
There is one source north of Toronto that has been around a long time, with an excellent reputation, that I believe is still in business supplying quality discus - and that is Upper Canada Discus - Bob Garside - who I believe still imports his discus from the known to be a high quality breeder - Wayne Ng of Hong Kong. Bob's operating location is somewhere near Barrie, Ont. I believe.
Look up his website up for contact details, etc.
As for the hero discus situation - isolating a single fish temporarily for QT purposes is not generally issue-producing. While a single discus may be a 'lonely camper' for that temporary period, there is no distressing condition to cause a solo fish any health- altering stress (e.g. bullying through pecking order development) - so not usually any problem.
Many hobbyists have said they've kept a single discus in a community tank for years without a problem.