You can re-use factory top hat or order new. I think most people are ordering the KYB from either Amazon or Rock Auto. RA has the better deal and you can find a 5% off coupon pretty easily (hint: tacomaworld.com).
Personally, I would change them regardless of miles on the OEM ones.
Locally there are a few in stock at around $575 or so plus a $25 coupon. I've skimmed through about 40 pages of this and it seems to be a nice purchase. Better quality ride? Its a direct bolt on, no other parts needed? Any other input would be appreciated, thanks