Ebay might be the best place for the Bunker Sudio parts, which are far, far more detailed than the Pit-Road or Yamashita versions, but also REALLY pricey. As in $70 for a set of five.

So, is your planned upgrade going to be in that strata?

FWIW, I do have extra Pit-Road turrets from the old E-5 set as well as the newer, Takao class specific E-11 set. Unfortunately, I've used all the barrels from the E-11 set, though.