would be a 5 min job in blender (any modeler really)

in blender load a B/G image of leaf

load a plane then subD a couple of times

move points around to make shape you want

then add thickness (soildify mod in blender)

 

if you dont like blender ;-) some dont lol

send me pics of leaf you like an some idea of how much detail, veins will push poly count up or I could do a low poly one and you can sculpt details in