(unless otherwise stated, please assume I'm only talking about normal MS)
There's only one 3 x 3 distinct MS.
There are 880 4 x 4 distinct MS.
With 5 x 5 MS, there are 275,305,224 of them. At a rate of one MS per second, it would take a computer over 8 years to generate all of the 5 x 5 MS.
Above 5 x 5 MS, nobody knows exactly how many MS exist. I think it's fair to say however, based on the explosive pattern with the 3 x 3 to the 5 x 5 MS, that even the most powerful computer in existence won't be able to generate all of the 8 x 8 MS in a lifetime, hence my warning.