A-Tech for Apple 6GB Kit (1x2GB + 1x4GB) DDR2 667MHz PC2-5300 200-pin SODIMM for MacBook (Late 2007, Early 2008, Early 2009), MacBook Pro (Mid 2007, Early 2008), iMac (Mid 2007) - Memory RAM Upgrade at Amazon.com
Install memory in an iMac - Apple Support
4GB NEMIX RAM Memory for Apple Module iMac 2007 - Newegg.com
Install memory in an iMac - Apple Support
iMac Mid 2007 20" Upgrade Kit - Real Mac Mods
Install memory in an iMac - Apple Support
Install memory in an iMac - Apple Support
OWC 16GB (2x8GB) ram Upgrade PC3-12800 DDR3L 1600MHz sodimm 204 Pin CL11 Memory Upgrade Kit Compatible with Late iMac, Mac Mini, and MacBook Pro Computer at Amazon.com
Memory Upgrades for Apple iMac 2007 - Up to 6GB
The infamous 2007 iMac on Catalina | MacRumors Forums