Ian Gambini found the first 2 SPSSs of this order in the 1990s. Jim Williams found 802968 in 2013. Brian Trial found 513 in 2014.
It is estimated there are approximately 3.2 x 10^8 SPSSs in order 40.
A listing of the known tablecodes is available spsso40.txt.zip. The file size is 63.5Mb