The question of the availability of "Lugers" during the Mexican Revolution is an interesting one. The following is taken from the 1908 Sears catalog:
It shows a M1900 for $24.45 - by the way, the most expensive handgun in the entire catalog by $4.45 - the ad also lists 30 Luger ammo for sale. No 9mm is offered. I have acquired the 1922 Montgomery Wards catalog too, and there are no Lugers for sale but you can buy 30 Luger ammo. 9mm is not listed.
While this isn't definitive proof about the type of Lugers available in the USA early in the 19th century, these were the two largest mail order firms at that time. I've got a line on a 1928, 1935 and 1941 catalogs - it will be intetesting to see if this changes and if and when 9mm starts to be sold.
John