Apologies in case I mssunderstand you, but there is the common misconception what "ppm" means.
It's nothing more than a concept to derive the "on hit chance" for a given enchant/weapon combination.
As such there is no need for "ppm" base for weapons with inherent procs (such as thunderfury, MSA).
It always comes down to a "on hit chance" ... it has to. Because a REAL ppm concept would require the program to see the future ... if you get what i mean.
I understand that. However, my testing showed that the MSA's proc rate is unchanged with various weapon speed/attack adjustments. Holding it in different hands, attacking with different weapon speeds, spamming hamstring with it in off-hand and main-hand, it still returned 1 proc for 10 swings.