You searched for "universal rectangular"
SPREADFAST
Heatsink, Universal Square Ceramic, 3.1 °C/W @ 400 lfm, 5.8 °C/W @ 100 lfm, 85 x 85 x 6mm, Adhesive, Screw
Part: SF-CHS-858506F
Large ceramic square heatsink for high-voltage electronics and power cooling.