I just buy it locally. When I make Colloidal Silver for close friends, they always give me a jug or two of distilled back as a thank you. Even still, I doubt my most volumnous year I made more than 5 gallons total.
Thats the reason why, unless you're all thumbs, just putting a cheap but functional setup together is usually the best approach. If you're only going to make a few gallons a year would you really want to invest hundreds of dollars on a device to make the stuff?
I realize the above is kind of a rhetorical question given the silvertron is no longer in production and there isn't anything that even came close to it but I think you get my point. Start out as simply and as inexpensively as you can and then, once you've aced the process and have a few batches under your belt, perhaps upgrade a bit but if you're like me, you'll realize for the minimal use per year of the equipment, its not worth spending anymore.
The first upgrade I would suggest if you started out with a silver rod would be to go to a silver bullion bar so you can up the current to 15-20ma so you can seriously speed up production. With a silver rod/wire, I doubt pushing it up over 10ma would be a good idea. Its all about surface area but you have to realize that with a bullion bar, you point one of the flat faces towards the cathode and the only real surface area that counts is whats on that side. The edges and back contribute a little but not nearly as much as you'd expect. Its perhaps a good idea for each successive run here, to 180 the bullion bar so every run is using the opposite side to keep silver loss on the bar even.
Oh yeah, make sure you flame clean your anode after each use. Some people just wipe off the greyish-black stuff after a run and they're throwing away lots of perfectly good silver because that stuff is silver oxide. Flame cleaning de-oxidizes the silver oxide and melts the resulting silver particles back onto the anode so you lose little to nothing. And given the random grainy nature of this remelt, thats what makes the anode start to look kind of a dull white color - thats silver and nothing but.