Well you can buy them directly from EngineQuest, also from Brian at IMM in California, from Hughes Engines, and many other places.

But first, back up, pardner!
You just CANNOT believe everything you hear. Many, probably the majority of Mag headed engines out there, have over 100,000 miles on them and are being used.
It's true that Mag heads have the tendency to crack between the intake and exhaust valves, but those heads came this way from running engines and the cracks don't leak.
Mag heads are not the best flowing wedge heads Mopar has produced, that used to be W2s. The mag head has three advantages:
1. Really good exhaust port.
2. Really good chamber as long as you get the piston up to zero deck or close.
3. Decent flow.
Now, porting can change anything, but no way would I pay money to get Mag heads ported. The EQ heads are better to start with. There are also RHS heads which come from a really good head manufacturer, but seem to be a little behind EQ heads out of the box. Then trailing back there are the Chinese copies.

So in closing, your engine will probably not develop external combustion because of the Mag heads, but there are versions out there that work better. They might be out of your financial grasp at the moment.

Get your vehicle on the road and have fun with it or it'll become a garage queen.

Follow the link below, they're the first head on the page.

http://www.aamidwest.com/index.php/enginequest/eq-cylinder-heads/chrysler-magnum-head/

R.