SpaceX will not likely beat 30 launches for 2018. Somewhere around 24 or 25 seems likely. As of this moment, there are six Block 5 cores completed with only B1051 having the upgraded COPVs that NASA demands for Commercial Crew. The seventh B5 booster is due to appear sometime soon and SpaceX will likely have 10 altogether before the end of the year. I fully expect to see a third launch of the same booster before the end of the year with B1046 being the most likely candidate. One of the upcoming boosters will need to be the B5 FH center core for there to be another FH launch this year (Arabsat).
There are nine older launched SpaceX boosters sitting around with one (Orbcomm 2) officially and permanently on display at SpaceX's Hawthorne factory. Two more have been given to NASA and Cape Canaveral for future display. That leaves six more just sitting around awaiting use in some form or another.
cores - spacex
Edit: It looks like the Commercial Crew delay cut into the number of launches for this year. Likely it will end up at 22. About half of those used previously flown boosters. My guess of 10 Block 5 cores is very likely going to be accurate. They have nine now with 2 1/2 months to go. SpaceX will have launched the same booster for the third time next month, likely the first B5 booster B1046.