I think there are a couple of solutions:
1) http://www.office-forums.com/threads/one-to-many-connector.49635/
or
2)
http://visguy.com/vgforum/index.php?topic=6953.0
If you google "Visio many to one 2013" or some similar words and order you will find quite a number of links.
Hopefully one of them will be applicable to the overall requirements of your network map.
Is it a network printer? If so, you really do not need to have a connection from every computer to the printer per se. Just place the printer on the network and identify it as a network printer. Then it can be understood that all computers on the network have or could have access to that printer.
Simplifies the drawing....
You can likewise google "network diagrams"...