There have been dozens of threads asking and answering this question over ther years. In the end, Google is unfortunately your best option as nobody will know exactly what you're looking for and there are more and more sites with textures every year (or month).
Of course, great textures typically have higher resolution than those that come with AC (and higher than AC can handle well - although Artlantis and CineRender in AC 18 can handle high res quite well)... and generally are not free. (Many free textures will be low res.) BUT.. have you checked all of the textures that come with AC? Most are not assigned to any material/surface, but are simply there waiting for you to use them.
See: ArchiCAD Library 17 > [TImg] Arroway-Textures 17
and ArchiCAD Library 17 > [TImg] Textures 17
for example to find LOTS of things that are not yet in any defined surface. In the case of the Arroway textures... you'll see separate images for the surface, and possibly bump, specular, etc The Arroway folder should give you some very good results.
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AC 28 USA and earlier • macOS Sequoia 15.2, MacBook Pro M2 Max 12CPU/30GPU cores, 32GB