I run a small community publishing shop and we occasionally have a couple hundred bucks free to contribute to good causes.
How can we send some $$ to the developers of Scribus?
The normal response usually is: You can't.
There is no organisation behind Scribus, the developers are voluteers and taking donations privately may have tax implications. And it is not money that is lacking, but rather time.
If you're publishing things and are using Scribus, you can send copies of a few works to Craig and or Jean...
They would for sure be proud : - )