Birks Custom Design is great -- it''s part of the Bloor Street Store. Mark Lash also have beautiful designs but I had timing issus with the eglington store. If you aren''t wedded to a timeline, this could be a good choice.
There are a large number of jewellers in the building at 21 Dundas Sq,. and not just the ones you see on the ground floor. Odds are you can find someone in there to do the job. They may ask you to purchase insurance for the setting of the stones.