This achievement should come through Career mode at some point but if you wish to boost the achievement you can drive at the test track in Canada on the map and drive along the landing strip with the big plane. There are 4 small ramps lined up behind each other and you can drive over them to raise the count. In order to not skip one of them you should drive no faster than 90 kph. Once all four ramps are taken, pull a slide and go back the other way. Achievement should pop in about 15 minutes if you do it this way.