The one I most commonly see is Geo Watkins Mushroom Ketchup -- and checking the ingredients, it is indeed pretty light on mushrooms:

> Water, Salt, Spirit Vinegar, Hydrolysed Vegetable Protein [Water, Hydrolysed Vegetable Protein, Salt], Mushroom Powder (3%) [Concentrated Mushroom Juice, Maltodextrin], Barley Malt Extract, Spices