Where are the grey knight names coming from?

[Scar Glamour]

I recognize some of them as knights from Arthurian legend such as Agravaine or Bors, but most are obscure to the point where even googling does not come up with any hits.

Is there a pattern or a source or did someone just come up with them off the top of their head? Because they did a better job than GW that's for sure.

[Mecha Wings]

I like Tarn because of the IDW Transformers character with the same name.

[⛧True Survivor⛧]

I'd say they're random names inspired by latin and ancient greek, but I'm not a 40k lore expert. The Grey Knights are obviously inspired by 12th/13th century medieval religious orders like the Teutonic Knights or Knights Hospitaller, so I guess they choose those languages because both were the most important in the liturgy of the western church during the high and late middle ages.