During the early 1970s, Zeus was being imported by West Coast Cycle Supply, who also handled Azuki, Nishiki and Windsor, though I'm not sure sure if they imported components in addition to the bicycles. By 1975, Zeus Cyclery Corp. had been set up in NYC. Zeus was aways available, though it was/is hard to find relative to the other major brands. In Europe it was a major presence, especially in the aftermarket.
As for Guerciotti prior to TSD, there was a company called Sherpa Designs that handled them in the mid-1970s. I'm not sure if they were an actual distributor. During this period many large retail outlets would purchase in quantity directly from the manufacturers in Europe.