I think there is another question separate to that of polar bear supply, and that is of enclosure design. Instead of designing hugely expensive enclosures which are often not that different to old school grottos - the difference, bar a bit of natural substrate and a bit more space, isn't that great, zoos should be more innovative with large meadows, lakes and wooded area. This would be a rich and stimulating environment for polar bears and could easily also house other species of bear or even ungulates or tigers if necesarry without looking out of place.