From what I know of All Balls Bearings:
has tables of bearing sizes that you can download. IIRC the table of steering head bearings isn't totally complete. But with the KTM stem you're stuck with one size.
99-3522-5 is a steering bearing 29 id, 50.25 od, 15 wide; this is a standard industrial bearing: L45449/L45410
22-1026 is a complete steering bearing kit, with two bearings (can't tell what kind, presumably 99-3522-5) three seals and an o-ring.