My girlfriend has a Quark Riken for sale if anyone's in the market for a power meter.
The vital stats are 172.5mm, 130BCD, BB30 - http://fudgescyclesonline.com/product/sram_quarq_riken_road_powermeter_crank_arms_bb30
It was used for one season on her old TT frame and doesn't fit the new bike. There's probably around 500 miles on it (and a small chip where the bike was knocked over at a village hall!). It also has the firmware upgrade that allows it to work without a frame magnet for cadence measurement. It's very easy to install and runs off standard coin cell batteries.
The Riken is a great power meter - the only complaint typically leveled against it is that it's too expensive, so at £450, there's really nothing not to like!
Let me know if you're interested or have any questions.