Oodle source is included in three zip files, located in
Engine/Plugins/Compression/OodleData/Sdks/2.9.0/src/oodle2_src_for_unreal_data_2.9.0.zip
Engine/Plugins/Developer/TextureFormatOodle/Sdks/2.9.0/src/oodle2_src_for_unreal_texture_2.9.0.zip
Engine/Plugins/Compression/OodleNetwork/Sdks/2.9.0/src/oodle2_src_for_unreal_network_2.9.0.zip
after cloning master branch and downloading dependencies.
But as mentioned previously, there are no project files, so you’d be on your own for how to turn that assortment of .h, .cpp, and even assembly source files into a library…