Here are links where you can find the PSE downloads Adobe provides:
PSE 12 Trial - http://www.adobe.com/cfusion/tdrc/index.cfm?product=photoshop_elements
PSE 10, 11 - http://helpx.adobe.com/photoshop-elements/kb/photoshop-elements-10-11-downloads.html
PSE 7, 8, 9 - http://helpx.adobe.com/photoshop-elements/kb/photoshop-elements-7-8-9-downloads.html
You also need your serial number to activate the installation. If you lost the disc and did not keep a record of it then your only other hope of finding it will be to check your Adobe account online.
Yo can try getting Adobe support to help with the serial number, but if you have no proof of ownership they will likely not be able to do anything to help you.
Serial number and activation chat support (non-CC)
http://helpx.adobe.com/x-productkb/global/service1.html ( http://adobe.ly/1aYjbSC )