I'm not familiar with the US products, but I remember that everywhere it was stated that VM&P Naphtha seems the way to go.
What I can just say it that the best Naphtha regarded overall is the one with the Hexane-Heptane-Isomer mixture, often labeled as C6-C7 or otherwise described as hydrocarbons with boiling range 60 - 80 °C. Just take a look at the ingredient section, maybe these data is written down - at least in Europe its fully labeled.
Too low boiling point like 40 - 60 °C will decrease DMT solubility heavily and also higher boiling stuff is quite bad, I saw one time that the freeze-precipitation step does not really work well if I recall correctly.
But you especially ask for the DEFAT step. Well the best Naphtha for the Defat step will also be the best one for the extractoin of your active ingredient later on. Or is there a special reason why you only ask for Defat?
Besides Mimosa Root Bark normally does not require any defat. Some "bad" bark may produce yellowish glue when not defatted. You would have to do 1 run without any defat and look if your product is crystaline or rather an oily mess. Then you know if you should do a defat all the time - that would save you a lot of work instead of doing a defat all the time, even though you may not even need it ;D Acacia species will always require defat, at least that's what is often written here.