iFixit sells Optical drives for that model of MacBook.
Depending on which exact model you have (Use our ID-Your-Mac tool to find out!) you can use one of these three guides:
Replacement optical drive compatible with all 13" Unibody MacBooks (Model A1278) Late 2008 or Early 2009 Unibody 15" MacBook Pros and Early or Mid 2009 Unibody 17" MacBook Pros. DVD-RW/CD-RW internal drive / 8x DVD read, 24x CD read, 8x DVD-R write, 4x DV — 12 available at 169.95 each.