Even though Valve thinks you shouldn't open up your Steam Deck, and they would prefer a professional do it, they will still offer parts through iFixit.
The team at iFixit recently did a video teardown, showing off things Valve suggest not to do as part of their announcement on teaming up with Valve for this. The good news is the wait won't be too long, as they told The Verge that parts will become available to order "this Summer".
If you want to be notified of when they become available, you can sign up to be notified.
Personally, I don't think I'll be opening up my Deck to fiddle around with its insides. I plan to mostly use mine as an actual gaming device, without any hardware adjustments. Will you be opening up yours though? Let us know in the comments.
If you missed it, Valve did their own teardown and it was quite good: