clenbuterol? triac? You could also try upping the doseage of ephedrine... Of course, these all come with risks.
You can assemble your own fat-burner that works best for you. You can buy your own yohimbine, ephedrine, caffeine, gugglesterone, l-tyrosine, synephrine, forskolin, etc. It may be cheaper to buy a preformulated stack and add whatever ingredients work best for you.
My personal favorite is E, C, l-tyrosine, sometimes some Y, and sometimes up the dosage of E and/or C.