greenleafnutrients.com The 300 gram bag is free except for shipping.
I'd try it first without the URB and see how it does. They still sell supplements from when they sold their old formula, but with the new formula you don't need them (and if you use too much you might add too much K and lock out N).
Even though you don't need them any more, it seems growers were still asking because they're completely unused to having one nute from birth to harvest. So they keep selling them to make the growers happy (and the accountants too
).