I'd like to find how to get the packages firmware-b43-installer and
b43-fwcutter in devuan beta.

I've searched for info in the mailing lists and I've looked at the main
Devuan site and the FAQ. But neither turned up relevant info[1]. The
packages should be available in Debian jessie in the contrib repository

https://packages.debian.org/search?suite=jessie&searchon=names&keywords=firmware-b43-installer

As a guess, I've tried adding the repositories like this:

deb http://fi.mirror.devuan.org/merged/ jessie-security main contrib

But the packages don't seem to be there, at least not for amd64.

Is there a way to safely pull packages from Debian jessie? Or are these
particular packages proscribed for any particular reasons?

Regards,
Lars

[1] I've tried several search engines but they keep changing Devuan to
Debian and even restricting to site:lists.dyne.org was not useful.