Yes, in ANSI layout, normal for springs to be missing for some of the keys :
Left Shift
Right Shift
Backspace
Enter
Space bar
Numpad 0
Numpad Enter
Numpad +
All of these, except spacebar, have an insert in the barrel instead of a spring, which the multi-wide key on top uses for stabilization (horizontal key stabs are centered, vertical key stabs are offset). The spacebar barrel is just empty - it helps with stabilization as is.
Yes, Unicomp will sell you an ISO keyset (in pearl/pebble, gray and probably even white). You will have to move the spring from the existing pipe key to the empty location of the existing enter, and you will need an additional spring/hammer for the left shift to split it.