The problem with Dept 56 lighting is the metal clip required to secure the bulb socket to the buildings. You can still find Dept 56 multiple socket cords on e-bay that have 3, 6, or 20 sockets per string. The 20 socket sets are somewhat rare.
On my permanent Christmas layout with 60 Dept 56 buildings I replaced the bulbs that were difficult to reach with warm white LED bulbs with bulb bases that fit the C7 Dept 56 sockets. The bulbs are available online or in stores, however, they are not inexpensive.
'Hope this helps.