@umlaut
Don't know if it's still relevant for you, but I did a quick pic-Google on 'bykort haderslev 1940", and this came up:
http://haderslevwiki.dk/index.php/Byvandring_i_den_gamle_bydel
The Copenhagen Library also lists something here, just browser search "1940" or German "Hadersleben" or "heereskarte".
http://www.kb.dk/maps/kortsa/2012/jul/kortatlas/subject206/en?notAfter=¬Before=&per_page=100&q=Haderslev+&search_field=all_fields
And this site might help you:
https://hkpn.gst.dk/
(Undskyld, at jeg ikke lige skriver på dansk ...)