Ukraine

If you want to expend a junker freighter, you can probably load it with containers of drones and sail it within range. Ukraine already dealt with hitting some long-range targets by having a container driven out to one filled with drones that they then launched. I'd guess that Vladivostok is probably easier to reach than things in central Asia, if you're talking UAV range.

searches for Soviet ICBM silo locations

https://alcpress.org/military/icbm/history.html

That cluster north of Mongolia is what I'd guess that the Kremlin likely considers safest.

Thing is, though, there isn't that much important stuff in eastern Russia. Most of the stuff that matters in Russia is in western Russia, closer to Ukraine.

For China and the US, most of what matters is in their east. For Russia, it's the west.