HI..
i bought mine @ www(dot)artworkfoto(dot)com. But it seems that they don't have for pentax mount any more. However you can check Ebay for similar model (same/different brand) from Hong Kong sellers.
The flash build quality is not that good. Mine is already spoilt. The battery holder can't hold the battery. The power is ok but tend to underexpose, youhave to compensate to get good exposure.
If i want to buy a flash, i WILL NOT buy this flash again, and save for better models.
I have tried the Sigma EF530, and think its far better model.