These "camps" were generally formed on an ad hoc basis, and had fleeting existances. There were likely scores, if not hundreds, of them throughout Missouri, with most of their names lost to history. And of those of which we know the names, more often than not we have no information on their specific sites. What were referred to as camps were essentially temporary bases--be they a base where men who were joining up were to report to, or a base where different regiments were to gather in preparation for a campaign, or a base where a single unit stopped and set up shop out of which they sent forays into the countryside. In essence, once you got a few soldiers together at a given site, or a thousand soldiers together at a given site, you tended to have a "camp."
There are a few clues to help us out in regard to Camp Stafford, however. The 2nd EMM was a St. Louis unit, and EMM units generally did not leave their home vicinity. And in looking at the muster card for the regiment's c.o., Col. Edward Stafford, we see that he was ordered into service at Carondelet on Sept. 27, 1864. Carondelet narrows the potential site down a great deal, but it still leaves the specific location unknown. Perhaps there is a comment in one of the St. Louis newspapers stating something to the effect that "Col. Stafford's regiment is forming at...." If you have the time and inclination, you could browse through the St. Louis newspapers and see if it is mentioned. If you're lucky, it might give the name of a street, or some other identifier. Microfilm exists for the time in question for at least three St. Louis newspapers--the Union, the Republican, and the Democrat.