Niner RDO, Whisky makes one as well.
Why do you want a 15mm thru-axle rigid fork? If you want compatibility with some wheels you already have and/or another bike/fork you already have, that's a good reason. Otherwise, IME QR's are better for rigid forks.
I had a chance to ride two Whisky forks back to back on the same frame and with the same wheels. One fork was QR, one had a 15mm axle, same geometry for both. The front hub was a Hope, so I just swapped endcaps and used it with both forks. There was hardly any difference in feel between the two. I mean very, very little - nothing like the difference with suspension forks.
The thru-axle set up was both heavier (~155g all in including hub endcaps, axles, skewers, etc) and $140 more expensive. If it were my money - I'd stick with a QR.
Here's the full article I wrote up on it: http://www.singletracks.com/blog/mtb-ge ... thru-axle/