Hi, sorry to hear about your planer.
I have used a dewalt like you have, it has a "universal motor", which spins at a mind-boggling speed, like 15,000-25,000 rpm. That means a small problem can become a catastrophe in a microsecond.
Still, are you sure isn't just the brushes worn out or damaged?
If they wiggle at all in their holders, replace them.
Brushes are cheap, just be sure you get all the carbon fragments from them out or you could cause a short.
I would use a qtip and water, GENTLY clean and polish the commutator with crocus cloth, being careful not to scratch the wire connections at the lower end of the commutator.
Wait, on second thought don't use the crocus cloth. If you get copper dust between the contacts of the commutator, it could cause a short or worse!
I bought parts once from M&M tools and machinery, service was good and I got good, honest communication.
It is a brick & mortar store in Salt Lake City that has been there for many years, I understand to have a good rep.
I have no connection with them and am sure there are lots of other great places to buy the part you need.
This link will get you most of the way to an online parts description and diagram.
There is a competitor a few miles away I have never gone back to because they weren't very helpful when I contacted them once. Just my one time experience, maybe others have had good service from them.
Google advertises for them so they get plastered all over the internet once you search for "replacement parts" for your dewalt. There name is very similarly worded to what I have above in quotes…
And of course there is the dewalt factory site:
Hope this helps.