I wrote this big long explanation about finding 1/4" loose bearings, then MCrider beat me to the post! In a pinch you should be able to find 'em and get 'er back on the road.
So instead here's a quick walkthrough of installing tapered steering bearings: I've easily done 75 or more of these installs on any of the big 4 Jap brands.
All Balls makes some good kits with OK quality (read: Chinese) bearings. They include easy to follow instructions for figuring stack height and spacer selection. Installation usually involves a spacer (thick washer) under the bottom bearing, to make up the height of the new tapered bearings being shorter than the old balls and races.
Drive the old cones out of the frame with a long punch. A few taps at different spots at a time - you don't want to cock the races in the bore.
Grease the new bearings. Put a gob of grease in your palm and force the grease into the race with a swiping motion - tough to explain, but easy to do. I've tried several bearing packer tools but haven't found any that work better than the old fashioned, albeit really messy way!
Stick the new races in the freezer overnight. I put 'em in clean baggies and stuff em right in with the ice. Once cold they'll usually drop right into the frame. A few taps should set them in place if needed.
A chisel and hammer usually makes short work of getting the old lower race off the stem. I use a pair of ancient wood chisels (don't tell my Dad!) and work 180 degrees apart. A few raps and it's off.
For putting the new bearing on the lower stem I use a piece of galvinized pipe I've had around for ever. Don't forget the spacer!!! Dust seal slides on next (if applicable) then the bearing. I've also used a length of an old fork tube on some bigger ones. Only hit the center of the bearing or you risk damaging it. On aluminum stems (modern sport bike) I freeze the stem but I haven't noticed any difference with steel ones.
Grease the surface of the stem. This prevents rust - it's not like it's going anywhere, but moisture can always find a way in!
Slide the stem into the frame. Install top bearing, then factoty dust cap and nut. I add 15 to 25 lbs. to the factory torque spec and tighten it down, then loosen and retorque to factory spec. This helps seat the bearings and cones.
Now put the rest together and go ride!
