A reliable synthesis of mesityl oxide is very easy to find.
While the synthesis looks easy, it does require rigorous compliance with the procedure.
Besides, a very volatile and quite toxic compound is created. Therefore, the synthesis should be performed by an experienced chemist or a student under the supervision of such a chemist in good laboratory conditions (above all, very good ventilation).
Mesityl oxide is flammable and its vapors form an explosive mixture with air already at a temperature of ~ 25°C.