Here is the rx100 hub (126mm oln, has both internal and external threads for both uniglide and hyperglide cassettes). It isnt cosmetically in great nick, but im not sure its actually been used.
£6 posted.
The spacer that jm mentioned takes up the extra space on the freehub required for an 8 speed cassette. It slots on the back before the 7 speed cassette. His hub looks in better condition than mine so no worries if you would rather go for his.