"In 1943, laboratory worker Mary Hunt brought in an ordinary supermarket cantaloupe infected with a mold that had "a pretty, golden look." This Penicillium species, Penicillium chrysogenum grew so well in a tank that it more than doubled the amount of penicillin produced. The deep fermentation method, the use of corn steep liquor and the discovery of P. chrysogenumby Mary Hunt made the commercial production of penicillin possible." --
http://www.herbarium.usu.edu/fungi/FunFa...

Aware that the fungus Penicillium notatum would never yield enough penicillin to treat people reliably, Florey and Heatley searched for a more productive species.
One hot summer day, a laboratory assistant, Mary Hunt, arrived with a cantaloupe that she had picked up at the market and that was covered with a ”pretty, golden mold.” Serendipitously, the mold turned out to be the fungus Penicillium chrysogeum, and it yielded 200 times the amount of penicillin as the species that Fleming had described. Yet even that species required enhancing with mutation-causing X-rays and filtration, ultimately producing 1,000 times as much penicillin as the first batches from Penicillium notatum.
http://www.pbs.org/newshour/rundown/the-...

Mary Hunt apparently worked for the US Department of Agriculture Northern Regional Research Laboratories (NRRL) in Peoria, Illinois, which was doing the work for the British from Oxford University. They had approached UK pharma firm ICI but they were already dedicated to other war-related projects and could not invest the resources in penicillin.

All of this underscore a fact we all may miss too easily: the modern kitchen has a wealth of common resources unknown to professionals a lifetime ago, such as ziplock bags and microwave ovens. Even your Mixmaster or Cuisinart would have been a wonder. You never look at those coffee filters, but they are, indeed, laboratory filter paper. Don't even think of hot and cold running water... the Brita filter... the controlled temperature refrigerator to people who only knew "ice boxes."

I actually tried that, and for weeks saw a whole lot of nothing. When I put it in some tupperware with the lid on the top but unsealed, and added some water, I got a lot more than nothing. In the post I have a lot of tips about where you can and can't get penicillin-producing fungus.