Hey there @vyzor! If you need specifically any non-top end hotfix version, you may need to build it from source. If you already joined the Epic Games team on Github, you can skip the first link below. If not, you’ll need to link your Github to your Epic account to be able to see the link to the 5.5.1 source.
https://www.unrealengine.com/en-US/ue-on-github
https://github.com/EpicGames/UnrealEngine/releases/tag/5.5.1-release