fuuma--- patent leather is not synthetic, it is actually leather that has gone through a special treatment/coating process to have a sheen. I am fairly certain all of the Lanvin sneakers have some sort of animal product on them. But I truly commend you ilaughed for being so committed to the cause!
I think basically the Lanvin sneaker craze was just that, a craze, and it has fizzled out. I still really love the ones I have, and intend to continue to wear them, but I don't think I would buy anymore at this point (kind of moot as it looks like s/s 08 is the last season for them anyway...).