Anderson also has a regular raisin wine recipe that uses two pounds of raisins and two pounds of sugar.
For he Madeira/Sherry recipe:
4 lbs raisins chopped or coarse ground
1 1/2 lbs sugar
1 gallon hot water
3/4 oz or 5 tsp acid blend
1 tsp yeast nutrient
2 campden tablets
3/4 tsp grape tannin
1 cup Madeire yeast starter
pitch the yeast when the must is 70 degrees
step feed with sugar syrup each time the must drops to 1.000 step feed to 1.010 until fermentation stops.
When fermentation stops cook in estufa for three months, fine, fortify and sweeten to taste; bottle age 1 to 2 years. Instead of baking flavor with Sherry flavor concentrate to make a "quick Sherry".
I did a quick Google search and I think you can find Sherry flavor concentrate.