Found some LEDs that SEEM to work in reverse

[ElectricDruid]

+1 agree with Rob. It's some astable circuit on a tiny wafer inside the housing.

You'd want to avoid the need for large cap values though (hard to fabricate on an IC) so I'm not sure what they'd use to get the fairly slow time constants those things typically have (100s of msecs, usually). Never wondered about that before.