Found these, but they're listed as out of stock:
http://www.tcscrawlers.com/Junfac-12...1-p-16232.html

These might work too:
http://www.tcscrawlers.com/Thunder-T...3-p-16234.html

From looking around, the popular larger wheels are 17mm. Keep in mind that running rubber that size on Axial axles is gonna be tough on the geartrain. I would imagine the stock aluminum locker will wear out pretty quick.