Customized helm-buffers-list in a new helm source

[fi nurr]

Hello all,

I would like to create a new helm source that lists all buffers where the major-mode is dired-mode.
I know I could use the regular helm-source-buffers and select dired-mode bufffers with the string *dired, but that
is not feasible in my usecase, as I would like to combine the newly created source into with other helm sources
(not a problem, have done it several times).

The question is, how can I create a new helm source or parameterize an already existing helm source
like helm-source-buffers so that only dired-mode buffers are show?

Thanks in advance!