New stamp pad ink

I had been required to do some document compliance and I have to buy a new stamp pad ink.  It is a small block of absorbent material saturated with violet colored ink. I bought the smaller and handy one just for home use. My brother uses it on his job application papers by filling in some finger print stamps using the pad. I often seen this kind of office supply only in the office and I thought of buying one for home because it is already necessary and often used.  The pad that I bought has already an ink on the absorbent cloth. In time of too many uses, it would soon dries up so I need to buy an ink that is specifically intended for the stamp pad ink.