You may want a Margarita punch, rather than poured magaritas. Poured margaritas will take a lot of bartenders. Rub the rims of the glasses with lime, and dip them in salt or lemon sprinkles before filling with the margaritas.
Here is one. This is for about 20:
1 liter Tequila
1 liter Triple Sec
4 quarts Sweet and Sour or margarita mix
1 quart ginger ale
1/2 gallon lime sherbet (optional) or additional quart gingerale
In a punch bowl combine the Tequila, Triple Sec, Sweet and Sour and ginger ale. Float the lime sherbet on top, if used.
There are a lot of variations; cranberry or rasberry margaritas, Malibu with coconut milk, and others.