I popped into Home Depot last Thursday and there were stacks of furnace filters and box fans available. Lowes and Ace Hardware websites show availability as well. Head down and take a look, YMMV in your area.
This isn't a nationwide shortage. Everyone in Seattle has been calling every Home Depot, Lowe's, and they've been sold out for a while. My local one in Bellevue was cleared out of all filters on Sunday, not even just the FPR10's. Ace's seems to be the most annoying. It lists a bunch of HEPA filters, then the product pages shows all of them are unavailable for pickup.
