If you want cubes, rather than a tub of powder, you can find Kallo organic vegetable stock cubes in supermarkets and smaller shops. Recommended.
Those are the ones I use.
Having used the chicken stock cubes, I hoped the vegetable cubes would be as good, but I cannot say I liked them. They taste a bit like Paxo. That might be ok if you are cooking rather meaty tasting things, but the taste is rather overpowering.
Vegetable stock is easy and quick to make. An onion, a couple of carrots, sticks of celery, parsley stalks, a clove of garlic (whole), some peppercorns, and there you go.
If you don't have the time or resources, then the Marigold powder is the most useful. Do be careful however. In a vegetable based risotto, for example, I use water, and a glass of wine, if I do not have stock. An easy stock cube can make everything taste the same, and somewhat salt.