Well look overseas for Glock 18 parts. Most TM Glock 18 parts such as the rear sight will fit on WE Glock 18s. The Glock compatibility between TM and WE are pretty close, but I am not quite sure if they are fully compatible. Look at the thread, "Upgrading your TM Glock" and you can find the compatibility. There are many upgrades/parts for the Glock 18, and you can find the reviews on the upgrading thread.
Example:
http://shop.ehobbyasia.com/shooters-...l#.VZzP0_kjYWA
http://www.rsov.com/product.php?prodId=14912
Other than that find that scumbag that scammed you, and report him or something. Or sell the broken Glock.