all org files from directory as refile targets (recursive)

[Eraldo Helal <eraldo@eraldo.at>]

I want to have all org files inside my directory "~/reference/" to be
refile targets.

~/reference/a/a.org
~/reference/b/b.org
~/reference/c/c.org
~/reference/c/c.ods
~/reference/d/d.org
~/reference/d/d.txt
...

I want all files ending in ".org" located somewhere inside (recursive)
"~/reference/" to be refile targets.
in the example it would be the files: "a.org" "b.org" "c.org" and "d.org"

I tried:
(find-lisp-find-files "~/reference/" "\.org$")
but I got the following error:
(error "Variable binding depth exceeds max-specpdl-size")

How (else) can I move a headline to a file that is not part of my agenda?
Any fix for my refile-targets issue?

Greetings,
Eraldo