I have an old computer with the mouse not working because the cable connector is broken on the mouse. The mouse connection is directly on the computer, not on the keyboard. The mouse connection(which is broken) on the mouse has 6 round pins and 1 flat pin. Where can I get an old mouse or an adapter from a USB mouse to the computer?
What your mouse has is PS/2 connector (Green):
You can search for what you need now that you know (PS/2 mouse).
If you have a USB mouse, you can convert it to PS/2 with a usb to ps/2 adaptor:
Again, you can search for a place to purchase for your particular area of the world.
A few PC shops in my area often have bargain bins for PS/2 keyboards and mice (albeit grotty, and yellowed from bromine flame retarding plastics). If they don't have them out front, ask them. Chances are they have one sitting around cluttering up space, that they would be willing to flog for a couple bucks.