How do i powderize herbs?

i am making my own lower bowel balance formula according to dr. christophers recipe. i would use one of the many on the market but i CANNOT do cascar sagrada and ALL of them have it in there, so i am making mine sans cascara sagrada but with all the other herbs.

my question is two fold. i can locate all the herbs but some i can only find in root or bark form, large pieces that need to be boiled or tincturized. i want to make individual capsules with dry powder.

so does anyone know how i can either grind the larger herb pieces into a powder? or does anyone know a good source of powderized herbs?