DMDO is not commercially available because of its instability. DMDO can be prepared as dilute solutions (~0.1 M) by treatment of acetone with potassium peroxymonosulfate , usually in the form of Oxone (2KHSO·KHSO·KSO).
The preparation of DMDO is rather inefficient (typical yields < 3%) and typically only yields a relatively dilute solution in acetone (only up to approximately 0.1 M).  This is tolerable as preparation uses inexpensive substances: acetone, sodium bicarbonate, and potassium peroxymonosulfate (commercially known as "oxone").  The solution can be stored at low temperatures and its concentration may be assayed immediately prior to its use.
The more active compound methyl(trifluoromethyl)dioxirane  can be similarly prepared from methyl trifluoromethyl ketone.