Ian Gambini found the first 2 SPSSs of this order in the 1990s. Jim Williams found 2662357 in 2013. Brian Trial found 882 in 2014.
It is estimated there are approximately 2.2 x 10^9 SPSSs in order 42.
A listing of the known tablecodes is available as spsso42.txt.zip. The file size is 226Mb