More or less directly opposite the hotel . A bit further along from the Hotel Riviera, go down the steps and there is a Tabac Shop . Or take a stroll into Malgrat and you will find a few there , or Calella you will be spoilt for choice as where to go

I know this is an old post but for future reference there is a fantastic tabac shop in Malgrat on Avinguda del Paisos Catalans at the junction with Avinguda de Barcelona. on the corner opposite the Hotel Papi.

there may be a better choice of tobacco products in that tabac, especially if you want cigars, but the one opposite the royal sun usually has many special offers ie freebies.
this is the one used by most of the tobacco tourists as the exchange rate for sterling is usually very good and you will normally get some sort of freebie with any reasonable sized purchase.
i believe the one at the papi also uses dynamic currency conversion, so using any card there will incur extra charges.

Good point; being a cigar smoker, I can't really comment on the cigarette side of things. However if you are a cigar smoker then this is definitely the place to go. The walk in humidor is superb and they have a lot of Edicion Limitada stock as well as some more obscure brands not found in many other places. They also stock Nicaraguan, Honduran and Canarian cigars, which is quite unusual for Spanish Estancos.

Yes they do use dynamic currency conversion - as with almost all the tobacco shops in Spain I have used - so you must ensure that you ask to pay in Euros and NOT in Sterling.
This is generally good advice anyway. Wherever you are paying by UK credit or debit card, always ask to pay in the local currency. (If they say you can't do this, then you have to either go elsewhere or decide if it's worth stumping up the extra.)

thanks everyone for all of your replies

steph x