Don't know the size but a bearing supply shop should be able to match you up with a generic sealed bearing. I'd bring in the hub/bearing so they can measure things. I've done this with all kinds of equipment besides bikes, they just take out micrometer/calipers to get bearing size then match things up. Might be considerably cheaper and/or better quality than the original too.

I've not been inside Mavic hubs but my guess is you can just tap them out with a soft metal (e.g. copper, brass) drift.

If you have luck post results/source so others can also be aware of alternative parts sources.