Professor wrote me a recommendation; I need another one with short notice but he hasn't replied
Speaking as a professor who writes a few dozen letters of recommendation a month (it seems like that, anyways), I would suggest that he is not ignoring you; he might be behind on his e-mail or simply preoccupied with other matters. 

I would recommend sending another polite follow-up e-mail, and barring that, drop by his office hours. 

Usually, the first letter of recommendation is the most work. Sending a second one is a lot easier, as your professor should hopefully just be able to make a few minor alterations and send it off to this opportunity.