While I entirely agree with you in how interesting the 1916 Punitive Expedition would be to model/wargame, a plate (#423)in an old issue of "Military Collector and Historian" (Fall 1975) shows the 7th Cavalry "tie-less" in the field; the enlisted men wearing canvas leggings reinforced with leather and cartridge belts for their Springfields. I think that you can find photographs of senior offices in a more formal uniform, and most or all officers in privately purchased boots. I do not know how difficult it would be to do the bandanas and tinted goggles soldiers wore in the field at this scale.
In addition to the new equipment you mention, I believe that I have seen at least one photograph of a motorcycle-equipped soldier on the Expedition. On the other hand, a note that accompanies the "Military Collector" plate indicates that for the sake of tradition, the 7th still carried their old brass-hilted 1860 sabers.
I have not seen it in many years and it may have been in black-and-white (I saw it on television), but a Gary Cooper movie, "They Came to Cordura" opens with a (fictional) large-scale cavalry action during pursuit of Villa in Mexico. There are publicity stills (in color) for the movie on the Internet, and it seems logical that there would have been old soldiers with living memories of the Pershing Expedition when that film was made in 1958.
Ironically, the often-criticized old Airfix/Hat WWI American foot soldiers have at least some of the appropriate equipment for 1916 Mexico--but, as you note, it was largely a cavalry enterprise.