depends, what kind of ingredients are you using? When I was a chef I used to say, I think , about 4oz meat per person (about 100g) so that is 4x100=400 0z which is 25lbs meat. whatever that is in grammes.
If only the irritating one from The Apprentice had asked here he may have won! On a more serious note- find a recipe for four and times it by twenty five as a guide. What type of curry are you wanting as a finished product and others might be able to assist, there are loads Thai, Bhuna ,Massala, basic chicken etc .........
But don't forget that you don't multiply up the amount of spices in the same way or it will be inedible. For example, if your recipe calls for 2 chillies for 4 people, don't for goodness sake multiply that up by 25 or people could suffer..........(!) You probably need to work on about half to two thirds of the total amount calculated, same goes for garlic.