BrowserUk,
I don't follow the results? It is my understanding that the results should be the multiples of all 3 factors merged with duplicates removed. Since the list is infinite, the list should be lazy only calculating what is needed. See Re: Hamming Sequences and Lazy Lists for my understanding an implementation of the problem.

Update: I still don't understand your output, but my understanding of the Hamming Sequence is wrong. I was so focused on lazy evaluation that I misunderstood "how do you generate the series of numbers composed of a given list of prime factors, where each can be used an unlimited number of times?" To me, that meant any positive multiple of any factor was valid.