RE: Where do i buy High density foam?
You probably won't find it on their websites but most places like Home Depot and Lowe's will have it in stock.
If you only need small pieces of it, you might want to try "dumpster diving" at building construction sites otherwise you'll have to buy large 4 x 8 foot sheets of it. A 2" thick piece of 4 x 8 will run you about $25.00 . Check to see if those stores have broken sheets that they can give you a deal on.
It can be cut with a hot wire, electric kitchen kife, X-acto saw or just a good sharp knife. I've used planes that are used to remove excess bondo from cars to shape it. Thin double-sided tape or an adhesive spray like 3M's 777 contact adhesive will stick it together quickly.