you can purchase a higher leveled version of the pre-order crystal from the pre-order crystal vendor found on the fleet.
Er yes, the next available level after level 7 is 47. No crystals for the levels in between, which is the problem.
@OP: While I understand the frustration, I also noticed that crystal stats aren't really all that important during leveling. I used the level 7 crystal until I could use the level 47 resp. level 50 ones. The loss of stats can be compensated though augments or higher quality mods (unless you level in fully augmented purple gear, of course, in which case the stats from the crystal don't need to be compensated because your gear is already overkill).