I ran into this problem the other day after adding yet another MFC device to our network. I added the printer to our 2008 r2 print server and added both x86 and 64bit drivers. But when I tried to add the new printer to the workstations that would be using it, it never showed up when scanning for printers. I double and tripled check settings on the server, made sure I had checked to box for “list in the directory”, but even after waiting several minutes it never showed up. I then found this forum post detailing a group policy setting that if left not configured limits the network printer scan to 20 twenty printers. After making the the changes all our printers are now visible when scanning for printers. So if you find yourself in the same boat you can click the link above to read all the posts concerning it or just do this from the group policy editor:

Go to Computer config
Admin templates
Printers
Add Printer Wizard – Network scan page (Managed Network)

Enable this and setup the types of printers you want to display. If you are like me and just need to show more network printers change Directory Printers to 0 (zero) for unlimited or to whatever limit you like.