Check out seedsandmore.net . They're in NFLD, and have a selection of tropical seeds. I've ordered from them before, quick service and the postage is low.

Some seed companies do sell tropicals. When looking for houseplant, concentrate on tropicals as these tend to survive well with minimum light. What kind of plants do you seek? What sort of lighting do you have?

Many catalogues such as Dominion, Stokes, Richters have a couple of pages of houseplants/tropicals for sale. Some also sell small plants by mail-order, e.g. Richters sells plants of many different scented geraniums that can be grown as houseplants. I bought clivia seeds from Park's in the USA many years ago, but there are cheaper sources of these seeds now. Why not try one of the other forums such as Canadian Exchange requesting info or seeds. I know there is a clivia forum and a violet forum as well. There may be a cactus an/or succulent forum as well.

there are Canadian dealers of Geraniums (http://www.holtgeraniums.com/, hundreds of varieties, that you cannot find at stores), Gesneriads (many vendors at http://www.avsc.ca/commercials.htm, from African Violets to miniature Sinningia), Orchids (http://www.chebucto.ns.ca/Recreation/Orchidcongress/vendors.html)....