I've updated my Hobby King large motor inventory checker:
Previously it had only the three "melon"-class motors, so-called because at 80mm OD, they are roughly the size of melons. (So called by whom? What kind of melons? Not watermelons...) These motors haven't been in stock at Hobby King in quite a long time, though they are starting to pop up in other places.
But there are other large motor candidates that are interesting to keep track of, including the brand new shiny SK3 line, which is the new "grapefruit"-class of 63mm motors. Somewhat dissapointingly, the SK3-63xx motors are actually 59mm in outer diameter. (The old 63xx grapefruit-class motors were truly 63mm.)
That said, tinyKart's older-model SK-6374-170 motors are falling apart due to poor construction and lack of a large radial can bearing. (And unrelenting abuse...) I will try replacing them with SK3-6464-190's I bought for a potential tinyKart swap a while ago. They have a can bearing and should be able to run to higher speeds without shaking themselves apart. They also weigh 1/3lb less, each. But, they have a higher resistance (37mΩ as opposed to 23mΩ), so they will generate more heat and/or less torque. Testing to come soon...
In the large motor category, there is also a durian class and a guava class that are relatively new and nicely-built. If you're interested in inexpensive RC plane motors that can be re-purposed into electric vehicle traction applications, this consolidated inventory list might help you choose.