[AndyB]

Extended Key Shaft: http://andymark.biz/am-0211.html
Matching Hub: http://andymark.biz/am-0077.html

Extended Hex Shaft: http://andymark.biz/am-0396.html
Matching Hub: http://andymark.biz/am-0096.html

Use the hubs if you rather not manufacture your own wheel. AndyMark wheels all come with a bearing bore for a dead axle setup*. Attaching the hubs to these wheels will allow you to run a live axle setup**.

Check out their sprockets page as well. Assuming you're using #35 chain, your choices from AndyMark would be:
http://www.andymark.biz/am-0166.html
http://www.andymark.biz/am-0167.html

McMaster has a larger selection of keyed sprockets if the AM ones won't fit in your design.

* - Dead Axle Setup: Wheels spin on a non-spinning axle
** - Live Axle Setup: Wheels spin together with the axle