I've only seen two different kubota keys: one that works in the smaller tractors (like the BX) and one that works in the larger ones (like the L). It actually works out well, since we have an L2850 and an L3250 at work, so instead of finding the right key, we just need a kubota key.
As a side note, the John Deere equipment we have have three key types, with the older quipment having one type (which I think may be the same key for some of Deere's heavy equipment), the newer equipment having another, and the 1050 tractor having a key I have seen on other JD tractors. I can start the 1050 with a house key though, but I found a masterlock key works better.
All the Toro equipment has the same key, from a snow blower to the $60,000 wide area rotery mower