You can actually burn the installer on a disc yourself for future use and safekeeping.
I'm not sure about the process for getting discs for an online purchase. There is something about replacement discs, but you'll need to get in touch with Support. Details here: http://helpx.adobe.com/x-productkb/policy-pricing/obtain-replacement-c ds-dvds-manuals.html
There might be some shipping+handling charges, I'm not really sure. The Support folks will know the details.
What piece of Adobe software are you looking for replacement media for? As Vikrant stated our support team can help you order replacement media. The only charge is for the DVD and shipping and handling.