Try
Busters at Queen/410. (Yes their site looks like they won't have anything but they seem to have a bunch of HID stuff the last time I was there) They had a GE HMAA highmast fixture there and some highbay parts there for sale. The highmast (347v? 750w HPS) was selling for $75 but it might be gone since the display disappeared. They did mention they had six so it won't hurt to ask. Make sure the fixture is for 120v though or you'd have to replace the ballast.
The highbay parts were around $25-50 and most were tri-tap (120/277/347v) 400w MH.
Other places you might find a signal or a streetlight for sale include: antique shops (I had the best luck in Waterloo area and Hamilton area), St Lawrence Market (Toronto, Sunday Market only), Kijiji/Craigslist (search traffic light/stoplight/stop light/street light/streetlight/streetlamp in buy & sell) and eBay. Restore does occasionally have HID lights for sale but I haven't seen a streetlight there yet.
Expect to pay $50 and up for a streetlight and $75 and up for a traffic light. If you want the traffic light to run like it did on the street you;ll also need to buy a sequencer for it. There's pretty nice model for sale on eBay usually for $35+$10 shipping.