Unless you specified something different, they should all be in the same folder. If you got your catalog settings you can discover the folder where the catalog you are currently using is located. Check that folder for the other catalogs. Also, File/Open Recent may provide you a list of the other catalogs for you to choose from.
In Lightroom, use File->Open Recent
In your operating system, you should have the operating system search for files ending with .LRCAT (might be lower case)
An easier approach is to combine these four catalogs into one, so you never have to search for the right catalog again, and you never have to switch from catalog to catalog again, plus dozens of other benefits.