Apple doesn't sell Tiger anymore, but you can buy Tiger, for example, on Amazon > http://www.amazon.com/Apple-Mac-Tiger-10-4-6-VERSION/dp/B000BWZZLG/ref=sr_1_2?ie =UTF8&qid=1358547508&sr=8-2&keywords=Mac+OS+X+tiger Also, it's very cheap to buy compared to the price when Mac OS X Tiger was released
"It bricked itself and won't go past the gray screen."
Are you certain that the hard drive doesn't have an electronic and/or mechanical problem? Has the internal battery on the motherboard ever been replaced? A very weak or dead one can cause startup problems.
As for the Tiger installer disk, buy the retail/universal installer disk (black with a large "X" across the face of it) and not one of the gray model-specific Restore disks. You can also check eBay. Note that the installer disk listed on that Amazon link is an upgrade disk, requiring OS 10.3 as a prerequisite.