What they mean by Nitrate is Nitrogen and the amount suggested is common and very negligeable, and the same with the Phopsphorus, very negligeable amounts. Nothing I'd concern myself with, just add more organic matter and those will take care of themselves.

Or if you do want to use the recommended materials, you can use 6 lbs. of ammonium phosphate (16-20-0). That'll give you 0.96 lbs of nitrogen and 1.2 lbs. of phosphorus. That will be close enough to do the job. You should be able to pick it up at a well stocked nursery or farm supply.