Stroke with only Pistons and Crank?

If the rod length is stock then the pistons must be longer to get the full stroke correct? If this is the case how do I calculate/determine the stroker piston length? Who makes these types of pistons? I have yet to determine the actual stoke as this is the preliminary fact finding stages.
Choose a piston for the stock rod length and whatever stroke crank you want. Simple, really.