There are no glasses that help you see lasers, only that help you retain yuor eyesight when working with lasers, and they are very important.
Beam visibility is a function of Rayleigh scattering, which dictates that shorter wavelengths scatter more due to the interaction with air particles than longer wavelengths, and the eye's receptivity to certain wavelengths.
Our eyes are most sensitive to blue, green, and yellow, depending on the ambient light levels, and the degree of dark adaptation our eyes are in.
Do you mean to say you need a laser which will have a very visible beam without any additional particulants in the air, or one which would be visible in highly filtered purified air? If you only need it to be visible without fog/smoke, it is a lot easier to pick.
For mounting outside at night in what is essentially an uncontrolled area (meaning people without laser training may enter the beampath's surrounding areas) you want to use the least amount of power possible for safety reasons. Stick to wavelengths between 473nm and 550nm, at power levels lower than 100mW. I'm sure 450nm would work too, but the beam would be less visible despite increased scattering because it is a bit far from the sensitive area of our vision so you would need to use more power, and that isn't the safest.
I really recommend you read up on laser safety, and if you intend to do this in any populated area research all the related laws and hazards. It may very well be illegal to use more than 5mW without a variance, depending on where you are.
I'd go with ~50mW of 473nm (DPSS Blue) or 488nm (Argon ION) if I were to be doing something similar. I'd only do it since I live two miles from the nearest sentient being, and I'd be damn sure of where the beam terminates.
