I do wonder if those ICs really are obsolete. I have two fake CCTV camera housings (one of which has a real camera inside now) that came with single-cell powered blinky LEDs using that very same IC (one had a D cell, one bought a few weeks later from a different store had a C cell). They were bought about 2 years ago but are still sold today, still with the blinky light to try and make it look more real-er. It`s possible that a vast mountain of them had been stockpiled though, and that the ICs
are now not avaliable new.
The one that wasn`t retrofitted with a real cam (and steady burning LED powered off the DC supply), blinked non stop for about 18 months on just one c cell. It still blinks now and then too depending on the weather, so I wonder if it`s actually just corroded contacts preventing it from working most the time? It
is getting kind of rusty round the edges now....