I don’t know about a web site, but I have it all spelled out in a rosary booklet I have. Here is what it says the Blessed Virgin said to Lucia:
"I promise to help at the hour of death, with the graces needed for salvation, whoever on the First Saturday of five consecutive months shall:
- Confess and receive Communion;
- Recite five decades of the Rosary;
- And keep me company for fifteen minutes while meditating on the fifteen Mysteries of the Rosary, with the intention of making reparation to me."
I think it’s up to you whether you spend the fifteen minutes in #3 meditating on the original fifteen mysteries, whether you bump it up and meditate on all twenty mysteries for twenty minutes, or whether you spend fifteen minutes on the twenty mysteries.
If you say the Rosary in a church (many parishes have a communal rosary after Mass on the first Saturday) and you add praying for the Pope on the same day, then you have fulfilled the requirements for a plenary indulgence as well, except for the complete detachment from sin part, which is the part I personally find difficult

. However, as I understand it (and I am not an expert), you can apply the indulgence toward one of the holy souls in Purgatory, even if you don’t have the complete detatchment from sin part–that part is their contribution, I guess.
–Jen
P.S. That is one indulgence per first Saturday, not one indulgence for all five.