Larry, I'm not Patrick but perhaps I can answer... You need to look carefully at the label, basically, and distinguish between Vitamin C itself (ascorbic acid) and its salts (sodium ascorbate, calcium ascorbate, etc.) They are not directly interchangeable in developers for obvious reasons.
Most health-food stores sell the acid form of Vitamin C, like your Rose Hips preparation, but I've found (by reading the labels) that many of the Vitamin C supplements sold at these stores are actually in the form of calcium ascorbate, the calcium salt of vitamin C. These are usually marketed as neutralized Vitamin C or "Ester-C" or things like that.
This use of calcium ascorbate is good for the body -- it should be less jarring to the stomach and also provides a source of calcium -- but no good for developers. As soon as you add this calcium ascorbate to a solution of alkali you will get a precipitate, various hydroxides of calcium (lime) or calcium carbonate (marble, chalk) etc.
I did manage to find powdered Vitamin C at a store called the Vitamin Shoppe or something like that. It was a chain and they had a few stores in Boston so I presume you may find one in Maine too. They sold powdered pure Vitamin C (no rose hips) in 200-g bottles for a reasonable price. I've been using it in Gainer developers with good luck.