I was wondering if there're any leaf-shaped punches for 1/35 leaves that I can use on brown/green paper.

Yep! Michaels craft stores has at least 2. Find the first one in kid craft sections where paper crafting/shaping tools are. Should be a squeeze type punch with a generic grape leaf-like example. It's OK.
Second one is also a squeeze punch tool and you will find it in the embossing/scrapbooking aisle. It is a Martha Stewart line item and titled 'Teardrop'. makes awesome leaves in colored paper.
Third one would be heart-shaped punches of various sizes that can be used for Ivy's,water lillys,and maybe Antheriums?
It's out there if you visualize it when you look at it. Just gotta cruize some aisles like a retard at Walmart sometimes ..............
Guilty as charged
Rick

Generic grape leaf(?) example: