Are you also using the Item Specifics on the left side of the Search page?
I looked for Stamps->Auctions-> Canada, but that was as far as the specifics would take me.
Then I looked at Chair->Auctions-> Canada but again that was the last refinement available.
But I am sure I have seen "within 50 km" very recently.
Are you only interested in Auctions? Because the distance may only be available with Fixed Price and perhaps Pickup Only.