Welcome!!
Where should I go?
Your location has a bearing on that and these are International English-language forums with members from all over. As your fellow end users, we have no way to "see" your location from your enrollment here.
If you give us a general idea of where you are, we can better answer "where..." inquiries. It does you little good if we recommend a service provider or parts source that is 3000 miles away or does not ship to your region.
That said, in the US, I would try PowerBook Medic for parts.
https://www.powerbookmedic.com/
Note on their home page they offer a 'send-in" service. I've used them before for older PowerBook parts. However, I've noticed that, after COVID, their inventory of parts for 20+ year-old Macs has diminished somewhat.
If you are up to tackling this repair yourself, search "powerbook G4 takeapart." That will usually get you good instructions and possibly a video tutorial or two.
Remember that there are at least 17 variants of the PowerBook G4 in three different display sizes. To that end, the PowerBook Medic site has a lookup function the twill return your exact SUB-MODEL to make sure you know what parts to order. Sub-model is super-important.
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