Look into directory where your Store Manager installed. Usually it is C:\Program Files\MagneticOne\Store Manager for ...\ - it may be different depending on your system configuration. Find Service directory inside, bridge.php placed here.

Also you can download latest version of bridge.php here.

Bridge.php can be used for osCommerce, ZenCart, osCMax, CRE Loaded and X-Cart store - one file for all carts.