I have found the finer grit paper 2K+ at my local auto parts store (Auto Zone).
You should be able to remove 2k sanding marks with a DA.
I use a 3"-3 1/2" backing plate and 4" orange CCS pad with M105.
If you can, follow that up with a 4" white CCS pad and M205.
What pad/polish combo do you have?
After the DA be sure to wipe 'em down with IPA before sealing.