Levi's Vintage Clothing if you really want that exact style. Otherwise, lots of retro-inspired stuff that's a bit more forgiving. That '50s style can be kind of hard to wear unless you're in very good shape.
You can have one of your current t-shirts altered. Fairly easy for a local alteration shop. If you want that brando look, and you don't have thick shoulder/upper arms, you may need to have the sleeves slimmed a bit, not just shortened.