Well, we do observe a lot of star 'deaths', and I would guess that with those come planetary 'deaths' also, includin gthose with atmospheres, and even oxygen atmospheres. These atmospheres, and their oceans, would turn to ice when systems fail, so there would be quite a bit of debris of such cataclysms out there.
And by the by, recovery of such ice would also offer the added dubious 'benefit' of finding weird and wonderful examples of long-extinct lifeforms from dead worlds. Maybe even sapiens. Maybe even preserved enough to regenerate? Such a find would potentially constitute property, so the PCs could come into pocession of an entire species or dozen.
Could even find all sorts of 'junk' in such an ice field from a long-destroyed civilisation that 3I scientists and engineers may give their right arm for.
Cheers
Greg