After a couple hours of research I found an ebay bike shop that sells brake pads for Cannondales with Helix hydraulic brake systems. Helix which is actually known as Bengal have the same part# as Hayes brake systems as well. The part # for Helix hydraulic disk brake pads on my 2013 Trail SL 4 29er is PH02.

X4PR TruckerCo s High Performance Disc Brake Pads Hayes Sole MX 4 MX4 GX C GX 2 | eBay