1) Did you get this from a friend? Call her and ask.
2) Search the gazebo section of online home improvement stores (e.g. Lowe's, Home Depot) for a similar model.
3) If the gazebo has any unusual features (e.g. if it's an octagon or has metal cupolas), Google gazebos and include keywords for those features.
I got a used self assembly gazebo or outdoor thingy with a screen, unfortunately when I got home there was no instructions or maker of this contraption. I no some parts are missing & I can order spare parts but how do I find out whos the makerof this thingy