No, they're abvailable to everyone and come in BIG numbers. What I've done so far with my finishing-to-50 Assassin and fresh new Agent makes it look like every bonus series rewards Major Experience Boost and there's at least 2 Minor ones on each planet either in class story or in class story+planet story. Often more (got 3 Minor boosters on Dromund). Then there are Boosters given for finishing acts. At this stage, I'm playing almost constantly with some booster enabled, either Minor or Major. Granted, if you only do class quests, you will miss on a lot of them but doing more is heavily rewarded, especially Bonus series that give Major booster. Also, you have to be smart about using the booster (activate it before having lots of quests to turn in then rush to do and turn in another bunch to use your booster to max), but it's still really rewarding, especially for F2P players.
I really feel like they did this thing right regarding F2P/Pref. Your Xp gain is nerfed, but they're trully giving a possibility to minimize effects of it, not just pretending to give you that with barely 2 boosters for entire game (like it was before 1.7.3)