I am looking to use my existing WD harddrive but use thunderbolt 2 instead of the usb3 A connection. I have looked for cables but all I find is type c ones.
Thunderbolt is a wholly different connection protocol from USB--it's more like external PCI-Express--so any such cable would need a USB controller built-in. It's almost certainly possible to miniaturize this into a single cable, but I doubt the demand ever existed for a commercial part to make sense; additionally, performance would still be limited by USB's capabilities. Your best bet is probably a Thunderbolt "hub", for instance this USB and eSATA model, or a larger dock such as this one.