The first thing to keep in mind is that your optical drive PBC is married to your motherboard. If you go and buy another optical drive off of Ebay you will find an error when you try to play any games because the new board is not the one for your motherboard.
With that in mind it is important to try and clean the one you have. The water damage does not look too severe from the pics you posted. Get some 90% + isopropyl alcohol and some q tips and toothbrush. Get the q tip wet with it and rub a generous amount on and around all of the components that are corroded. Then get them good and wet again and take the toothbrush and brush them. This will hopefully get the board working again.
As far as the cable is concerned you can find them on Ebay. There is a wide one and a skinny one so be sure to get the correct one. If you look on the bottom of your board you will see a 010 or 020, as far as I know the wide cable goes with one of those numbers and the skinny cable goes with the other. Be sure to ask the seller which cable it is and maybe even get the measurement just to be sure.
I hope this helps.