The office is in the very centre of the historic centre of Florence:
1 min. walk south from Piazza Repubblica
1min. west from Piazza Signoria and the Uffizi gallery and
2min. north from the Ponte Vecchio.
95% of first-time patients find the office without bother.
The remainder can struggle for a variety of reasons:
often the piazza is not mentioned on tourist maps as it is quite small, but has a long name.
confusion over the naming of the piazza:
the name on the sign on the street is 'Piazza Mercato Nuovo'
the official name used by the postal service is 'Loggia del Mercato Nuovo'
The nick-name used by the locals is 'Loggia del Porcellino' in honour of the statue of the bronze boar.
If you are asking directions from the locals or taking a taxi it is best to ask for the 'Loggia del Porcellino' otherwise you may be directed to/taken to the Mercato Centrale about a mile away.
OK, so you have found the piazza, where is number 1 (black)?
The piazza being a square has 4 sides.
No. 1 is on the east side.
i.e. if you are looking at the face of the boar with the H&M shop behind you then No.1 is on the right side of the square (the same side as the ice cream/chocolate shop: Venchi).
Last but not least.....
Cars are not allowed in the centre. The closest parking spaces are: 1) train station, Santa Maria Novella, 2) a private garage on via Ghibellina, near the Bargello museum.