Argon ion lasers are large, very *HEAVY* critters that require a lot of power (prepare for a 20mW unit to draw close to 16 amps on a 120 volts AC circuit); they also have cooling fans that make a noise like a soft vacuum cleaner motor. After extended use (greater than 20 or 30 minutes), they can heat a small, unventilated room to temperatures beyond what most would connsider "comfortable".
Argon ion lasers come in four primary flavours: single line single mode, single line multimode, multiline single mode, and multiline multimode.
I have a single line single mode unit; outputting 18.4912mW at 488nm in the blue-green region of the spectrum, with a TEM00 beam. And yes, the beast is fairly noisy and consumes ~16 amps of power.
If you want an argon laser that lases at multiple wavelengths simultaneously, look for a multiline version. The visible laser lines most commonly available in an argon ion multiline laser are:
457.9nm
476.5nm
488.0nm
514.5nm
528.7nm
To seperate the beams from a multiline laser, I believe all you will need is a glass prism.
Here is an illustration showing a few laser transverse electromagnetic modes - the single mode laser produces a TEM00 beam which is shown on the left here.
Hope you found this to be at least somewhat helpful.