I also use carmelized onions (lots of them) in places of recipes that call specifically for a broth that made with oxtail, which gives the broth a pretty rich and sweet taste. It worked pretty well for me.
i'd go with marmite. tragically its probably not easy to get that in some places either though.
It is in Fred Meyer which is owned by kroger. BUT for some unexplainable reason, it's over by the almond paste and tubes of icing.
I am NOT about to tell them what it really is for fear they'll upcharge it by another $5 and move it to the "foreign foods" section. Or worse, decide that Bovoril is fine enough and discontinue the stuff completely.
If you have a Kroger-owned store near you, check over by the baking goods section, but look c-a-r-e-f-u-l-l-y because the jar is pretty hard to spot (in my store, it's almost at the bottom - maybe 1 or 2 shelves up but no higher than that).
Also, regular Worcestershire sauce has anchovies in it, but the Kroger store brand doesn't.
I make mushroom stock to use in place of beef broth. I fill a pot with a few litres of water, two bags of dried mushrooms (variety mix), a bay leaf and some pepper. Bring to a boil, simmer about 30 minutes, strain, and cool. It's very hearty.