okwen,

If you are looking for a tartan specifically to wear with brown leather accessories I would suggest when looking looking at tartan swatches that you ignore all the Modern and Ancient colors and focus only on the weathered versions.

From my understanding of such things the weathered tartans are all somewhat muted and really lend themselves to brown leather accessories and daywear outfits. This might help to narrow down your search a bit.

Cheers

Jamie