What do you do when even a fast lens like the FA-35mm/ƒ2 is not enough and you don't want to go into high ISO (1600 or more)? Especially if you rightly find that the built-in flash is far too small and underpowered (NG is 12) — not to mention too close to the lens axis?
You buy yourself a real flashgun with a rotating head (both horizontal and vertical direction is better)... There a several to choose from, being Pentax own (360FGZ and 540 FGZ), Sigma 500 DG Super or Metz 58 AF-1 which has everything including wireless support and is cheaper (and easier to get compared to the Sigma).
(with apologies to Scott Adams, quote taken from a Dilbert cartoon).
I finally took the Metz 58 AF1 flashgun. While I still struggle to use it properly as flash photography is not easy, it is useful and can save your day, especially if you can bounce the light above or on the side of the subject. Direct lighting is often too harsh.