Hello EEs

I am looking for a military grade thermal pad/heat sink.

Issue: Think of an enclosure (box) that’s 5x5x5” and on the inside holds a PCB board that has a lot of heat coming from these power supply’s.

I am looking for options to dissipate some heat from the PCB board.

I don’t have much experience in this. Aside from general knowledge of there are some pads I can add. But any specific military grade I can use or best option to add something to remove the heat from the PCB?

I have some components on the board that are getting so hot it’s shutting down my board due to the rating of the part.

This is basically a batch until I revise the design.

Thank you very much for your input