Hello,

I am trying to add a few spells granted by a subclass I'm homebrewing (Just recreating Aberrant Mind Origin) and have everything right except when trying to add certain spells (Arms of Hadar, Dissonant Whispers, etc) they do not show up, while other different class spells do, including ones that need to be added. 

I can add them to my list to learn (they will count towards known) on the subclass basic information page, however when trying to grant them and not count towards the known limit within the subclass they do not appear to be available.  I have tried to make a separate feat or item to add them but they do not show up on those drop down lists either.  Any suggestions?

Both of the spells you listed are found in the PHB, but not the free Basic Rules. If you have not purchased the PHB from this website, you will not be able to add them to any homebrew the way you are intending. If you have access to them through content sharing, your PC will be able to learn them the normal way as long as they are in a campaign with sharing enabled.