These can accommodate for 3 TO3 power transistors each and lots of other pre drilled holes for TO220 and other TO power devices.
Ceramic Transistor Insulators HeatSink 2mm TO-3 TO3 Transistor Pad (5 pieces)
9 TO 220 Power Transistor Heatsink With Cooling Fan From Military Test Gear
Insulating Transistor/Regulator shoulder bush, TO3/TO220 devices pack of 10
IRF130 International Rectifier Original Transistor TO3 N-MOSFET. FREE P&P
Large Aluminium Heatsink For TO3
Various Sizes Aluminum Heatsink Heat Sinks IC Chip Transistor Black Silver Gold