All permits through Inyo National Forest, including all Mt Whitney permits, are only available online through recreation.gov.
The old process does not exist: Waiting in line and then asking the desk ranger if anything is available. This year, and likely from now on, you need to keep refreshing the page on rec.gov, and hope that a permit will come available. I've been told by Inyo staff that no-show permits do indeed show up online this year.
For day hike permits, the no-shows should become available the day before. As I write this (12:45 pm), there are two day hike permits available for the
Main Mt Whitney Trail for tomorrow. Curiously, there are no overnight permits currently available, even though there were quite a few during the walk-up process.
