Bearings are easy to find. Check your LBS, look in the yellow pages for bearing suppliers, or just look online. The bearing number will be printed on the seal on the side.
Don't just soak them in WD40 especially without removing the seals. If you want to do it right look up info on repacking sealed bearings, or just replace them.
Yes, take the freehub apart, clean it, grease it, and put it back together. Use a lighter weight grease for the freehub like Slick Honey or so. The internet will find you directions on taking it apart.
Use a proper degreaser like Zep citrus stuff, or the Finish Line products. Don't use WD40 for anything on the bike except for perhaps some cleaning. It's pretty much only a solvent but not anything you want left over or to be lubing with.
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