You can get 2.
> One from a house in Veilstone. To get there face the steps of the game building (where you collect coins) and go left there should be some steps that lead to the gym. After you have got to the top of the steps turn right and there's 2 houses. The massage is in the first house.
> The other one you need to have beaten the pokemon league, have access to the resort area, and have a pokemon with 10 ribbons (easiest is 7 daily ribbons from Sunnyshore, 1 from footprint man (he's in a house on the beach near I think it'd R113 west of the motel), 1 from beating the pokemon league, and 1 contest ribbon from Hearthome). Once you've done these requirements go to the ribbon syndicate and on the next floor up talk to one of the women (these massages are better than the Veilstone ones).
EDIT: Or you could do this. After a massage save the game then turn it off. Set the clock on the DS to 23:59. Wait a minut then you should be able to get another one.