[Arran]

I've bought them from an outfit called WJOE radio myself, Just Radios is a bit expensive even for a Canadian shopper as they tend to sell so called "kits". The trouble with buying kits is what happens if whomever is packing them makes a mistake, either puts the wrong values in, or leaves a few out? In addition to the places Terry mentioned, and WJOE, you can also get them from Mouser and Digi Key, but you have to figure out their search engine first, they have caps made in all sorts of package styles, and materials, axial lead is what you want for restuffing, radial if you don't care about restuffing or are restuffing a block condenser. If that .04 uf is on the power line you may want to use a safety rated capacitor, ditto if it's on a tone control with the cap connected to the B+.
Regards
Arran