You don't really see men in traditional Japanese clothes in Tokyo anymore.
Literal
Japanese-clothes appearance [possessive-の] men [topic-は] Tokyo [in-で] [topic-は] already not-much not-see.
和服姿 uses the suffix 姿 (すがた, 'figure, appearance') to describe someone's outward look when wearing Japanese clothes. 見かける ('to catch sight of, see around') is for incidental observation. もう~あまり~ない ('no longer much') marks a decline. A culturally observant sentence about modernization.