I have a habit of loosing small things so I usually just make some with a little cross connect wire and some 8p8c plugs.

Make them female with a gender changer.

To make a T1 loopback you just run a wire from one pin to the other as follows:
1 - 4
2 - 5

A 56K loopback is this order:
1 - 7
2 - 8

Also makes a cross-over cable by the left column of pins terminating on the other jack to the right column of pins. IE Pins 1&4 terminate to pins 2&5.