My first and only car currently is a first generation Lexus IS300
I don't know everything about them, but I wish to document as much as I know about them
Aftermarket ball joints are likely a perfectly fine option but if you wanted OEM parts Toyota sells a kit with the ball joints, castle nut, and cotter pin.
The part number for this kit is 04436-53010
This kit is not available through Toyota USA or Lexus USA, you will have to import this.