<?php
$key = '<removed>'; // from http://steamcommunity.com/dev/apikey
$file = file_get_contents("http://api.steampowered.com/IEconItems_440/GetSchemaURL/v1?key=$key");
$json = json_decode($file);
header('Content-Type: text/plain');
echo file_get_contents($json->result->items_game_url);