Irix now has a US based distributor (www.irixusa.com) and the Irix 15mm f/2.4 lens is now listed directly for sale on Amazon US (Irix lenses have been available for a while on Amazon UK, Amazon DE and Amazon IT). The US prices are:
Irix lenses are available in Nikon, Canon and Pentax mounts.
Via NikonRumors