As far as I know there is no other bearing conversion that will work.
I did a fair bit of research on it a few years ago and found diddly squat.
Here is the bearing interchange.
FORK HOLDER BEARINGS (LOWER)
FITS 74-76 78-91 KX250, 80-81 KX420, 83-04 KX500, 83-94 KDX200, 81-84 KDX250, 84-87 KXT250 - 92116-1008
FORK HOLDER BEARINGS (UPPER)
FITS 84-87 KXT250, 74-76 78-91 KX125 KX250, 83-04 KX500, 75-76 KX400, 80-81 KX420, 78-84 KL250, 80-84 91-94 KDX250, 83-06 KDX200, 97-05 KDX200, 79-80 94-96 06-10 KLX250, 93-96 KLX650R & C - 92047-017
You do have some option.
You can use any year kx500 fork and corresponding triple clamp on your bike.
Or, you can get a steering stem from Emig racing and press it into a set of triple clamps from a KX450F and run something new, perhaps even a set from a KX250F but I'm not certain. But, a call to Emig would fix that.