You can obtain the molar absorptivity of any unknown solution by preparing different concentrations of solution and measure their absorption in certain wave length. Slope of carve is molar absorptivity     

For the cyanidin-3-O-glucoside, the molar absorptivity is known for the solution 1% HCl in methanol (ε  =  34300  L.mol–1.cm–1), and for the cyanidin-3-rutinoside, it is known for the solution 1% HCl in water (ε =  28840 L.mol–1 .cm–1)

thank you very much; this paper could help, even though, unfortunately, pelargonidin and its acylated derivatives are not present in Vitis vinifera (or present in trace amounts!!)

ciao

Alessandra