The AeternoBlade Switch demo has five NintendoWare for CTR/3DS source texture files.

\system\ui\layout\textures\gp_tscreen_bg01_1.ctex
\system\ui\layout\textures\gp_tscreen_bg01_2.ctex
\system\ui\layout\textures\gp_tscreen_bg02_1.ctex
\system\ui\layout\textures\gp_tscreen_bg02_2.ctex
\system\ui\layout\textures\pause_tscreen01.ctex

Odd, cause the 3DS .ctx textures aren't even in 3DS image formats, but b5g6ru unorm or so.