Today I was trying to service my headset on my 2016 Felt Z95. When I took the bearings off (caged ones) they just fell apart when I tried to clean them. How do I go about finding replcements? Thanks
The balls are loosely held in normal cages, so once you determine the exact size of the bearings (typically imperial measurements e.g. 3/16"), you can buy replacement ball bearings at a bike shop. The shop will be able to verify the bearing size if you bring one or two along. Sometimes the upper bearings and lower bearings on a headset use slightly different size ball bearings.
If the cages themselves fell apart, in practice they are not required, and you can just put in the new set of ball bearings without them. Cages can make the process more convenient, and your local bike shop might also have replacements for those.
In terms of purchasing ball bearings for headsets, keep it mind:
Replace all the ball bearings at once, with new replacements from a single manufacturing batch. This ensures the balls are exactly the same diameter, not different from batch-to-batch variation or previous wear.
The quality of the ball bearing in terms of roundness and smoothness is graded, with a smaller grade number indicating less deviation from perfection. Grade 25 or grade 10 is what I usually get, and I would try very hard not to get worse than grade 100.
Buy a few extra bearings just in case you drop one and it rolls away; if you are getting rid of the bearing cage, there may be room for one or two more ball bearings than before, another reason to buy some extras.
If you don't already have some sort of bearing grease, I find "marine boat trailer wheel bearing grease" to be cheap and VERY effective. In the US a number of brands are easily available at auto and marine stores, home improvement center, etc.
There are many good headset bearing service instructions online. Park Tool has generally very good instructions; their non-video section on the bearings of threadless headsets is here.
Heatset bearings are rather small, (second-smallest bearing-balls on a bike after the freehub) so there are a lot of them.
IF you manage to find all the escapees, it is possible to reassemble them into the retainer cage. The trick is to clean all balls and the cage first, and then insert a ball into each space, and use needle-nosed pliers to slightly-squash the metal tongue so it retains the ball, and does not bind on the ball.
This presumes the cage is undamaged. If cage is dead, then it is possible to assemble a headset using grease to retain the balls, but without a cage there's a good chance all the balls will migrate to one side of the race, and you'd need to add more anyway. This is a dirty-hack and later-you will be mad at present-day-you, the next time the headset comes apart and all the bearing balls fall out again.