To follow up on my previous answer, I asked about Doh replacement on Penguin's private forum for purchasers of this effect, and I wrote to Penguin directly. The Penguin rep gave me a link to replace the Doh at a very nominal cost, which I posted in the aforementioned forum. In other words, if you purchase this effect, it shouldn't be difficult to find all the Doh you need to perform it for as long as the gimmick lasts, which should be close to indefinite, as it's solidly constructed.