500 Series Racks/Fenders are not available for separate purchase.
The rack and fenders are only available as an add on at the point of sale.
It is always possible to order 3rd party racks and fenders on your own after purchasing your 500 series.
There is a Ride1UP Facebook Owner's Group which has a lot of great resources for accessories that are confirmed to be compatible by other riders.
With the 500 series, it is necessary to order a rack designed for disc brakes:
FENDERS: When purchasing the right fenders for your 500 Series it may be best to visit your local bike shop. If you prefer to shop online, please verify that it has the hardware required to be installed on your bike. You will want a minimum width of 55mm to ensure good coverage.
Often during installation small brackets are used to attach to the fork or axle. Your local bike shop likely has the hardware needed and fenders that they can mount to your bike taking out some of the guess work:
These are just a few examples of the hardware you may need for your fenders. Often it comes with hardware, but may not include everything you need. If you cannot make it to your local shop and want to shop online SKS provides many mounting hardware options and quality fenders.
Eyelets for fenders