the .pat files are the regular DSM OS files from synology. You can download the DS3615xs, DS3617xs and DS918+ build 24922 versions, which are the ones most commonly referred to in polanskiman and IG-88's installation guides, from here: https://archive.synology.com/download/DSM/release/6.2.2/24922/
(For other versions you can go to the parent directory and select the one you want. Do not go to the 6.2.3 version unless you know what you are doing (e.g. you know your hardware is natively supported by the DSM version as there isn't a working extra.lzma available for 6.2.3 yet afaik.)
Make sure you download the correct one for the bootloader. So DSM_DS3615xs_24922.pat, DSM_DS2617xs_24922.pat for the two Bootloader 1.03b versions or DS918+_24922.pat for the 1.04b bootloader
Also make sure you read this thread for upgrading to/installing DSM 6.2.2 using Bootloader 1.04b/1.03b: