I get the feeling many people don’t know how to search a shoe you want.
If it may be for sale anywhere in the net,
what have all the offers in common?
They all use pictures of the shoes.
So your best bet is to use the Google Picture-search.
Type in the name of the shoe and look.
If you don’t know the name, try getting that first.
Best choice are pics from shops (obviously)
but in my experience, blogs often have links to shops, too.
If the search doesn’t give you any options or all are sold-out,
you better check Ebay or the other sites for second-hand pairs.
You will always get a Air Max 87 AMS or other rare shoes,
because some people never wear them to sell later.
But your average general release has bad chances of being found after the time on sale racks since nobody buys them to sell later.
They are bought to be worn and abused.