I search for aquarium plants on Ebay and find lots of suppliers. You can also google aquarium plants and they show a long list of suppliers.

Home Depot has recycle area where folks bring back their empty plastic pots/containers after they plant in soil. I pick up all my seed starting pots, containers for free from there.

I managed to find almost all the large black pots I wanted by asking businesses that were putting in cedar trees if I could have the empty pots (Cedar trees come in fairly large and heavy pots much of the time). Many restaurants that have an outdoor dining area will do some sort of landscaping - if they're putting in big plants, that means big pots. Lawn/landscaping maintenance companies often have large pots in the back of their trucks, or know of places you can get them. City gardening trucks are worth asking too. I framed my request politely and carefully - I wanted them to want to give me the empty pots and be happy to do it. I was interested in keeping things out of the trash... Recycling/reusing the big pots was much better... I would come get them... Please call me when they're evailable... BP

I don't know, I never buy shrubs. But how large are you looking for? Do you want a particular color, or just a fairly tall lilac bush? I probably have some you could dig up, most of mine spread. I am less than 1.5 miles south of Milwaukee County! My lilac offspring are probably fairly tall but not very bushy, as they are growing next to other bushes. Marcia