There are definately alternatives to meat for him, but its finding what he will eat.

Dried fruit like sultanas, apricots are good.
lentils
tofu
cereals that are fortified are good as well.

Matilda didn't eat well at all, she would eat little tiny bits throughout the day. I have no idea how she survived!! I made sure every meal had bites of iron in it. Matilda also has the milk allergy which caused her to be unable to absorb foods, so it seems that no matter what she ate she wouldn't have absorbed much!! Vit C helps absorb iron, and probiotics can help absorption as well ,which is why In-Liven is good.

I would even suggest taking him to a naturopath. They can usually help with finding out what is causing stuff with him its hard to figure things out isn't it?