Does such a beast exist?

X-fusion Trace is a 120mm 15mm 29er fork, but what do you want it for?

Something like this? http://www.chainreactioncycles.com/manitou-tower-pro-forks-29-tapered-steerer-2013/rp-prod71593

Otherwise I have a 120mm Reba with 20mm axle…

I have X-Fusion Slides, seem very good so far.

I’ve just been through this process. I ended up buying a Manitou Tower Pro from CRC – was £234 last week, now £211!

The reviews are very good – stiff, light, reliable, and plush.

Other options :
X Fusion Slide – £300 from Loco
Rockshox Revelation – old models £300 ish on CRC
Rockshox Reba/SID – beware new models can’t be internally travel changed anymore – a new damper cartridge is needed.

You can get both Reba & SID in that flavour.
29″ SID 120mm new for 2014 I think though so not filtered through to the cheap OEM guys yet. The Germans have 29″ Reba’s for around £320 not seen much stock in the UK though as have been looking myself.

RCT3 SID looks like a lovely fork but is £500!

You can run a Revelation RCT3 at that too.

Another Slides owner here, been really pleased with them so far. Stiffer than you’d think and just seem to be really well made compared to Fox/Rock Shox equivalents.

Magura TS8 R120?