Mantle of the Force was created by Exar Kun during his experiments with Sith Alchemy. It was one of the items kept in his laboratory on Yavin 4 and was rediscovered by Suvam Tan. (Originally I think the devs wanted it to be Exar Kun's lightsaber crystal, but this was changed in a comic)
Heart of the Guardian was one of the Jedi artifacts that Exar Kun and the Massassi plundered from Ossus during the Great Sith War.