Any bearing supply can get them. The serial number is on them. The supplier can also tell you how good the type of bearing is.
Now the fun part.
Removing the spindle. Hahahaha
The noise you are most likely hearing is that the spindle has worn marks from the bearings. Whether it's from time, or spindle not sitting straight. It happens.
Make sure all the screws holding the spindle/motors box are tight. The goal is not to twist the box removing the spindle.
Remove the chuck and backing plate.
Remove the belt pulley.
Put a towel over the motor.
Block the right side hole(chuck side) with a towel or paper towels. Put a bunch of ice inside the spindle and block the hole. Wait a little bit. The ice will cause the spindle to shrink a little and use a big rubber malet and go to work. The spindle slides out towards the tail stock. Once you get the spindle to move 3/4 of an inch, you'll see the burn marks. Obviously, clean the mark on the left side because it still has to go thru another bearing.
Yayyyy, it's out. Clean the marks, don't sand to much. Install the new bearings. Where the marks are on the spindle, add some center punch tits. Put fresh ice in the spindle and get it back in place.
Good luck
Have fun.
Note*
You might be able to use a gear puller. I don't remember if I did or not.
DO NOT TWIST THAT BOX!