I've been in 7 or 8 across Ontario, they seem to be pretty plentiful in areas of urban sprawl (i.e. where new subdivisions are being built over what used to be farmland); probably because Wal-Mart can sell flowers way cheaper than them. That'd be your best bet to search.
I really love abandoned greenhouses personally cause they feel so massive inside (kinda like abandoned factories but less security).
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Unfortunately I don't know your location so that's all that I can say, good luck though.