without having any specifications on what you are doing... what is it?, how big, how long is it going to be running, torque requirements, how precisely this thing need to run a 1 hz, etc...
assuming you mean RC servos...
1- How consistent are servos i.e. Do they keep constant speed/time? servos are generally for positioning something not driving around and around, they have three input wires, two for power and one for a position input. the position input will work with the servo's internal controls to make the servo turn to a specific place in it's 180 degree turning range and stop there. but you will need to supply the digital input electronics.
2- How much torque do these motors have? It will be operating several different gears simultaneously and I don't want it to slow down during the times where it has to move multiple gears at once. you can get them in different sizes so finding one with enough torque wouldn't be a problem, but it might take some experimentation
3- Can you power servos straight from the wall? I plan to have it wall powered, not battery powered. No, RC servos run off of 5 VCD, the 120 VAC out of the wall would need a wall wart (~$10) or something to drop the voltage down to a useable level.
4- Where can I get a quality 1RPM servo from? servos are cheap and plentiful, just search amazon or hobby town or any other hobby store website and take a look, there are ten million to choose from, servos are generally rated in degrees per second, so you are looking for a 6 degree per second servo, but servos only turn 180 degrees, they generally don't go around and around
servos like in RC car servos don't turn a full 360 degrees around, they only move back and fourth thriough the same 180 degrees. With a micro you can program one to teeter-totter back and forth fairly precisely in 30 or 60 second intervals to drive some other mechanism like a cam, but you can't go around and around. and you may not want to drive it like that indefinitely... You can hack a servo by removing the potentiometer and replaceing it with two resistors to make a simple high torque one way or the other motor, but you will have no speed control. or you can hack out everything but the motor and have a high torque little motor that you can control the speed and direction of, but you will have to supply the control electronics. also these motors are probably not rated to run continuously and may burn up after a while. of course you can always but one somewhat bigger than you need and since you are running at less of a load than it is rated for, it may last forever.
maintaining a constant speed on a small DC motor that can run continually would be difficult. you would need to run the motor at a higher speed and gear it down through a gear box to create the torque, and you would need some kind of speed feedback, digital encoder (?) to adjust the speed as the load changes.
if you decide to run the thing off of 120VAC, you might steal a motor out of a microvave turntable (fairly slow and torquey) and gear it down as necessary... but the absolute speed may depend on the outlet voltage which may rise or dip depending on the neighborhood circuit loading, it may speed up during the day when everyone is at work, and slow down at night when everyone is at home cooking and doing laundry and the grid dips... BUT it may not be rated for continuious use and burn up after a few days. right now I am looking at the oscillating fan on my desk and I think that that oscillator motor might be a possiblilty.
but if you can't kluge in somekind of a fan-oscillator motor or hack a servo, if you have a fairly unlimited budget, what you probably need is a STEPPER motor, but you will need a microprocessor (or a stepper motor control chip) to control it. Driving a stepper motor with a micro lets you control exactly how fast the thing turns, and often they come with a gear box attached so they put out plenty of torque. thiese are the motors they make CNC machines out of so you can get very precise control , but $$$.
My final suggestion would be look into doing a two resistor servo hack on an oversized servo to get rotation one direction at a fairly constant speed and playing with some gearing to get the speed right. you would need someone who can solder to do the hack (its actually pretty easy if you have the equipment) then if you know sombody with electronics experience, they should be able to whip up an input signal with a proto-board and a 555 timer chip and a few components. you may be able to use a cheap servo tester to drive it in the right direction with essentially no electronics experience necessary. if the tester plugs in to the wall, you won't need a wall wart... winwin. good luck
servo hacking - YouTube
http://www.instructables.com/id/Drive-Servos-with-a-555-timer-IC/
Amazon.com: servo tester
also servos can be pretty noisy... you may need some sound dampening, or go with the fan oscillator.
this is the fan I'm talking about, haha they have them at walmart.
http://www.amazon.com/Lasko-4916-De...d=1400520459&sr=8-6&keywords=lasko+table++fan