Sal is the capacitor guy. For coupling caps. You can buy one or a kit. You might do a kit, if you are going to get into this heavy. I like to use 630 volt coupling caps for everything except low voltage applications. This prevents your having to stock capacitor of several voltages. Just order whatever value you need at 630 volts for coupling caps.
http://www.tuberadios.com/capacitors/For the filter caps, I would use Mouser's. Their website is hard to navigate, but just put "Nichicon PZ" in the search box. That will save you hassle. You will want 47uf @at least 450 volts, 500 would be better to replace the 40's. Use 33uf @ at least 450 volts for the 30's, and then get a 47 uf@ 50 volts for the cathode bypass cap. If you use Nichicon PZ's you should be able to put the three high voltage caps back in the can, then mount the cathode by-pass cap down in the chassis. I can talk you thru that if you'd like. This will make a nice neat installation and you will learn a lot. I'll be happy to help anyway I can. The only stupid question is the one you don't ask and it gets you into trouble. Good luck.
http://www.mouser.com/Electronic-Components/?utm_source=bing&utm_medium=cpc&utm_campaign=Brand%20US&utm_term=mouser.com&utm_content=Brand%20MouserI would strongly recommend your going with Nichicon caps in that Magnavox amplifier. If you were a little more familiar with this stuff, I would have you hot-rod your power supplies like someone was good enough to share with me. That might confuse the issue. You can always go back and upgrade after you get a bit more experience.
Have you verified that the power transformer is good? If it is fried, you are wasting your time doing anything else. Like washing and waxing you car after the engine blows up. If the transformer survived this, you might consider fusing at least the primary. It probably will not save the transformer in the next "short" event, but it might save your house. Something to think about. I fuse all my Magnavox instruments when I tune them up.
I found several pictures of how I re-stuff a can cap that might help you. This is the tuner on my Concert Grand. First, I mark, then cut the cap can in half. I take my fist and rip out the old guts. They come right out with a twist. Then I bore small holes by the original connections. You run the wires thru the holes and connect them to the terminals. Use radial caps for this purpose, I forgot to mention that. Put the halves of the can back together and seal it with chrome HVAC tape. You can't tell you've been in there. I take a felt-tip pen and put the date on the top of the can that I re-stuffed it.