Let's see where is the observation that nature never makes only a single thing of a kind...... that might be in Lucretius rather than On The Nature of the Gods....
I would say this eliminates a "single god" from Epicurean consideration as well:
Lucretius 2:1077 -
[1077] This there is too that in the universe there is nothing single, nothing born unique and growing unique and alone, but it is always of some tribe, and there are many things in the same race. First of all turn your mind to living creatures; you will find that in this wise is begotten the race of wild beasts that haunts the mountains, in this wise the stock of men, in this wise again the dumb herds of scaly fishes, and all the bodies of flying fowls. Wherefore you must confess in the same way that sky and earth and sun, moon, sea, and all else that exists, are not unique, but rather of number numberless; inasmuch as the deep-fixed boundary-stone of life awaits these as surely, and they are just as much of a body that has birth, as every race which is here on earth, abounding in things after its kind.
[1090] And if you learn this surely, and cling to it, nature is seen, free at once, and quit of her proud rulers, doing all things of her own accord alone, without control of gods. For by the holy hearts of the gods, which in their tranquil peace pass placid years, and a life of calm, who can avail to rule the whole sum of the boundless, who to hold in his guiding hand the mighty reins of the deep, who to turn round all firmaments at once, and warm all fruitful lands with heavenly fires, or to be at all times present in all places, so as to make darkness with clouds, and shake the calm tracts of heaven with thunder, and then shoot thunderbolts, and often make havoc of his own temples, or moving away into deserts rage furiously there, plying the bolt, which often passes by the guilty and does to death the innocent and undeserving?