Where can I get 98 Jaguar xk8 caster shims?

 

Just get 1/16" and 1/8' standard alignment shims and open/cut the 'mouth' to increase the diameter of the 'U' shape to fit the larger castor bolt.(the standard shims will not fit over the bolt)
I threw the washer type shims away when I noticed the original ones were mismatched/missing from the bolt.

The factory setup is specific to RHD or LHD so I just inserted the correct sizes for my LHD when I had it apart.

This U shape is easier to adjust than the washer type if you need 'tweaking'. (loosen, swap, replace)

 

Good advice from Bob, and additionally, I would also add some similar 1/32" shims to the arsenal.

 

Original there should be 4 shims in total, each side of the car. Two of them are 0,9mm thick and two that are 1,6 mm thick. Nothing more, nothing less. Adjust caster by moving shims, not remove or add anything.

 

I think I used 1/32 and 1/16 shims as that is close to the metric shims OEM.
1/32 is close to .9 and 1/16 is close to 1.6.

Been a while since I had the suspension apart but it was missing shims and they were in the wrong places.
I put the 1/32 and 1/16 shims in the order for LHD cars.

You can swap them around to increase or decrease castor if something is bent or out of spec to get it closer to correct.