I believe Simplehomenet had it somewhere, but I could not find it.
I know SubRoutine. An Insteon developer has it on his site.
JLT:Soft also has it
I would pick the latest -308. As it is what I use with my 2414S; 2414U and 2814U PLCs.
If you are using a PLM 2412S; 2412U; 2413S or 2413U. SDM3 would not be needed or used.