If the leaves on the one you're thinking of were properly leaf shaped, greyish and soft, then its probably Cytisus battandieri - if they were linear, like needles, it'll be Cytisus praecox. The first has a strong and sweet fragrance - the second has a very faint, not so sweet scent. Either are readily available either online or at garden centres. Both require a sunny position in free draining soil, and in the case of Cytisus battandeiri, a sheltered spot at the back of a border - it can get up to 20 feet in time.

I have noticed this as well driving through France. I did wonder if the high temperatures made the fragrance more noticeable there.

Of course, it could be Cytisus Racemosus or Spartium juncium...although the latter can get to 14 feet tall....as can C. battendieri