Nick,
Yep, that is correct, the old 17" MOs are only available in 5-spoke, with the exception of the new 8x17s 6-spoke, which are currently ONLY available in this rim width . However, I don't think they will produce any different rim widths, as the spoke design would reduce the capability of accepting big brakes if the wheels were any narrower.

So you are limited to either the 5-spoke 17s all round, second hand old style 18s, new style 18s or making the new 8x17s fit like on your mates...