Finding unknown names

I need help!

Half sisters will be Awen and [name]Jael[/name].

Need a name that meets these requirements:

Has a formal name and nickname possibilities
Not in the top 1000, is relatively unknown in the USA
Not Biblically based
Preferably Danish (Norse/Scandivian), [name]German[/name], French, English, or Irish in origin (Other Celtic language might also be ok, like Scottish, Cornish, [name]Breton[/name]. Welsh maybe, but trying to stay away from it since Awen is already Welsh).
Preferably starts with an S
Preferably does not start with an A or a J
Is a name with a history of being used as a name, not a recent invention or a noun only recently used as a name

It doesn’t need to fit ALL of those requirements, so give me your best picks even if they only meet 4 out of 7 or something. Here are names already on my radar, some of which I really am not keen on giving, most of which don’t meet all the requirements above, but there was something about them that I did like.

[name]Adelaide[/name]/[name]Adelheid[/name]
Behrte
[name]Brighid[/name]/Birgette
[name]Dagmar[/name]
[name]Dagny[/name]
[name]Delaney[/name]
[name]Dorthea[/name]
[name]Heidrun[/name]
Lente
Margretha
[name]Mathilde[/name]
Rigmor
[name]Saga[/name]
[name]Sanne[/name]
[name]Saskia[/name]
Segolene
Seine
Sidse
Sigbrit
Sigilinde
[name]Signe[/name]
[name]Sigrid[/name]
Sigrun
[name]Sloane[/name]

Any tips to finding unknown names?

Thanks!