Kolb sold kit ultralight aircraft that were assembled by the buyer, who could use any name if wanted to incorporate the ownership for FAA registration. The deadline has passed for registration with N number in America of old ultralights. In June 2005 company owner Norm Labhart died in a crash of a Kolb Mk III Xtra.
The New Kolb Aircraft Company is listed in the Kitplanes magazine 2012 Kit Aircraft Buyer's Guide and does still offer the Mk. III Xtra, as well as the Firefly and Firestar kits. All three are billed as "LSA Legal" but further research by you is required as to whether or not they would meet or have met the ASTM Light Sport Aircraft standards. They would be registered as Experimental class or E-LSA if qualified.
Contact them at www.kolbsport.com or (606) 862-9692
They are apparently still in London, Kentucky.