See the document at the link below and jump to pages 10-12 to identify your year and the possible blank options. Then find the corresponding image towards the back of the document and verify which blank matches your existing key profile.

https://www.google.com/url?sa=t&source=web&rct=j&url=http://www.ilco.us/media...

Many local locksmiths will carry the ignition key, but the fork lock blank can be harder to find in stock. My locksmith had the fork lock blank and said it was a "forklift" blank, but it worked perfectly.

Note that this reference document is only when you have your existing key in hand and want to order a blank to then go have your local key shop cut it for you. If you lost your key all together, you'll need to take another route such as taking proof of ownership and your lock key code to either the locksmith or local bike shop to have them see if they can cut a key per their database. Make sure you ask about cost up front. Something as simple as a lost key for a truck toolbox can be upwards of $25 or more.