The 6 wheel blocks from the Aristocraft and USAtrains six axle diesels are all in this range if you delete the centre wheels, but none are exactly 150mm.
The simplest solution would be to take an aristocraft A29355 block from the class66 and friends, and remove the centre wheels (you can do this from outside), leaving the end axles with a wheelbase of about 144/145mm. It's also the most expensive.
Somewhat cheaper would be a similar idea based on a USAt block (R22-422 from the SD40-2 or R22-625 from the SD70, the main difference between the two types is wheel diameter), but this is more complex in practice - you need to diassemble the block to remove the centre axle, and add some external framing to lock up the block's hinged joint. getting it all back together with the internal UJ's lined up is a swine.
Neither of the above is suitable for R1 curves, they are really only happy on 4ft radius (LGB R3) and above.
Similar surgery on a USAt PA block or Aristo E8 unit will liberate something in the 160-165mm area.
The longest unit I can think of that's R1 friendly is the 6 coupled block from the Piko Br80 tank - removing the centre axle is fairly simple, and the end result is 114mm wheelbase.
Jonathan
RDE