How soon is production art available?

[tarakatsuki]

I'm assuming that genga/douga/etc are still being done for anime that is currently airing right? They haven't changed that process over the years? If so, I was wondering when do those sketches generally become available on the market for new shows? With Yashahime being released earlier this month, I'm hoping I can get my hands on something of Moroha at some point