And those were only created by Davros from his own genetic material, and presumably a lot of scrap metal. Not an easy task when you have only one good arm and one mad Dalek to help. And he was only around because mad Dalek
So what I'm thinking is that when the Dalek horde claims to be all the Daleks there are, what they mean is they are all the Daleks in this part of the galaxy, and there are lots more Dalek hordes elsewhere.
At the very least I think they must have some automated assembly line cranking out little Dalek shells as needed. I see it as some massive spaceship, slowly travelling through space swallowing ore-rich asteroids and stripping out everything it needs to build more Daleks, just waiting for Davros, or the Dalek Supreme, or whoever is in charge of any given horde, to send in an order for five million Daleks to be dispatched to the front lines.
And another thing; given that the Daleks are supposed to be the most formidable force in the universe, when was the last time we actually saw a planet they'd conquered? I guess it's just possible they mine them for parts and move on, except for the ones they fit motors to and pilot around the galaxy for shits and giggles, and maybe play conkers with them, but I'd still like to see that side of them. It would be a nice change to see Daleks that aren't either front line troops or upper management.
EDIT: It occurs to me that the Daleks shown in Asylum of the Daleks were described as the Parliament of the Daleks, and while skipping past the notion of the Daleks having anything like a democratic society, I am left thinking if all those thousands of Daleks are only representatives of many more Daleks, then my theory of multiple hordes seems to be borne out by the show.