Kashmiri chilies are large chillies with relatively mild hot taste and is known for its bright color that it imparts to the recipe.
How to make kashmiri chillies paste.
To use raw whole kashmiri chilies always soak overnight or boil (1 minutes only). Then blend with few garlics, cumins and vinegar (preservative) to make a smooth paste. Store in fridge. Use recipes as desired. Check recipe of Kashmiri lal mirch chicken.
These chillies and easily available in indian stores and buy whole chillies and make paste for better taste.
To substitite kashmiri chillies use
1/4 tbs of cayenne papper and 3/4 tbs of paprika for every 1 tbs of kashmiri lal mirch.
Although, the taste will be different as kashmiri chilies have very distinct aroma but this will also give a good flavor too.