How to get rid of maltese tears stains?

Have you tried using Google?

I came up with this site:
Maltese tear, eye & face stain - Frequently Asked Questions about tear stain (http://www.malteseonly.com/tear.html)

Also, I think that you'll get better answers in the dogs section of the forum. :)

Tear staining has multiple causes, you need to try and determine what the reason for the staining is first.

First reason is dietary. High protein diets can often cause staining around the eyes and mouth.
Try switching to a lower protein food and see if it reduces the amount of staining.

Second is eye conditions. These can be anywhere from excessive weeping caused by the structure of the eye, to irritation and allergies.
If the dogs eyes are weeping simply because of structure then there is not much can be done about stopping it from happening.
Allergies on the other hand can be managed by finding out what is causing the irritation. Household products, are likely culprits.

To remove the staining that is there now I would recommend a product called Eye Envy.
It is a liquid you dab onto the stained area followed by a powder. It can be expensive but works very well.
Tear Stain Remover | The Safe and Effective solution for Cats and Dogs by Eye Envy (http://www.eyeenvy.com/)

I have a Japanese spitz puppy and have been giving her a teaspoon of apple cider vinegar in her drinking water, and giving her filtered water instead of tap water. I find that this has reduced her tear stains! Apparently the minerals in tap water encourages tear stains and apple cider vinegar changes the ph of the dog's body preventing the bacteria/yeast causing the tear stains from forming.