The same companies that manufacture car tires-- Goodyear, Bridgestone, Michelin, and probably most of the other major manufacturers (but those three definitely all have aircraft tire businesses).
About $6000 per tire in the one source I found, which lasts anywhere from 2 to 4 months depending on how many times a day it lands. Bridgestone manufacturers tires for the 777 but it’s not clear if they made the one that fell off
They're probably not cheap.