How can I get more umami in a veggie burger? I'm not a vegan, so let me get that out there as the first sentence. I can find recipes all over the place for veggie burgers, but all I've tried have been bland. I may indeed have an umami flavor addiction. 

What are your pro tips for great taste in a veggie burger? To keep within the scope of the question, let's say that at least 75% of the weight must be made of things that would be considered vegan. Items must be available to a foodie in non-boxcar size quantiles through regular sources (though not necessarily "common" or "everyday" sources.) 

I'm looking for items, not recipes.

I think I'm going to tag this question as "vegan" so 100% vegan answers are welcome too and will be up-voted.
Umami comes from natural glutamates. Two excellent vegan sources of umami are tomato paste and dried shiitake mushrooms (rehydrate then mince). Fresh shiitake aren't nearly so high in glutamates. They are available very inexpensively at Asian groceries.

If you want vegetarian, but not vegan and can find a rennet-free parmesan-style cheese, they are also very high in glutamates.