Well remember all you need is 999 pure silver, so you can use silver wire which you might be able to get from electronics shops (try privmsging some of the guys here who use silver wire to see where they got theres from). You can also go to jewellery repair stores and see if they'll sell you some of theirs. Pawn shops that have coins may have some. Also try ebay, just search for: 999 silver. Just make sure it's 999 pure, if you're not sure then dont buy it.
I just used a Mint because the purity is guaranteed and because there's one in my city so I had them post it out to me. But even if there isnt one in your city just find one in your country and they'll post it to you. You can even buy from overseas mints but obviously youd be looking at more $postage. I don't know where you are, but if you're in the US I'd guess that there's a Mint in every state? Just try Googling or using the Yellow/White Pages, youll find one and they should have a website too, probably also with an online shop. Then just call them/send them an email saying you need 2 x 1/2oz 999 pure silver in any form (coin, ingot, nugget etc - coins have best surface area tho, along with silver wire)
Another option, just search Google for places that sell Colloidal Silver generators, and instead of buying the generator just buy the silver rods/electrodes which they often sell seperately.