As a practical matter, just about any sort of epoxy will work. Some just work better than others. Arctic Silver works the best for your appliaction with Arctic Alumina coming in at a close second.

I mess around with this stuff so much that I've abandoned using the hard to find/get stuff. I use plain old two part epoxy and mix it with aluminum oxide powder. I add enough to make a paste then just apply it. It works really well.

You can get aluminum oxide powder at any hobby shop that caters to rock collectors. It is usually called lapidary compound and is used to polish rocks. Just get the finest grit that they have. It should look about like baby powder and is sold in 1lb bottles and should go a long way.