I also pick up some things from HD and Lowes but I really buy mostly succulents. I guess it depends what you consider houseplant before you decider what and where you could look to buy certain plants. Most houseplants are just tropical plants that cannot grow outside in the winter for your zone.
Are you looking for something specific? It is usually how I pick a vendor to purchase a certain plant. Plants are starting to be sold like you do doctors now days. You have to look for specialist for certain plants.
