According to my knowledge, there is no sepearate lookup component against Office 365 profiles etc. However, I think I found a workaround to get around your challenge of making a people picker you can place wherever you want on a PowerApp Card.
(assuming you have access to create a SP List and connect it with your PowerApp in your scenario)
I would suggest creating an additional "dummy" gallery and "dummy" edit form, but we're really only interested in showing a dropdown visible on edit form which act as an independent "People Picker" against Office 365
Details:
1) Create and connect to an SharePoint List with just one User Column
2) Add an item with a Random User ( this will show up as default in the people picker )
3) Add an additional "dummy" Gallery and call it SPLookUpGallery. Set its "datasource" property to the SPList
2) Add an additional "dummy" EditForm and call it for example "PeoplePickerDropdownForm"
3) Set the "item" property of the EditForm to to SPLookUpGallery.Selected
4) Hide the dummy gallery by setting "visible" to false and remove all fields "Dummy Edit Form" except People dropdown
5) Do some neccessary GUI adjustments to the dummy edit form until you only see the People Dropdown
5) You should now have an people picker independent of any existing Galleries or Edit Forms
It should be now quite easy to reuse the selected value where ever you want:
Like: [DataCardValue Dummy Edit Form].Selected.DisplayName <--- Click on the dropdown to get the name
Now the selected User value ca be used for example in filters/ lookups or other components on the card
and not just in an selected item in edit form connected to an gallery in use. ( thus the trick with the dummy gallery/ form )
