Hey, Peter. Don't know exactly what you mean by locking IEC (since I don't believe such a thing exists).
But if you are looking for just a good snug fit quality-built IEC connector, you might try:
1. A Hubbell 15 or 20 amp IEC from Jena Labs that is cryo-ed.
2. A Marinco 15 or 20 amp IEC from Cryo-Parts which also have a pretty good fit.
Both of can brought much improved sonics because of the cryo-treatment as well as the snug fit.
-IMO
But if you are looking for just a good snug fit quality-built IEC connector, you might try:
1. A Hubbell 15 or 20 amp IEC from Jena Labs that is cryo-ed.
2. A Marinco 15 or 20 amp IEC from Cryo-Parts which also have a pretty good fit.
Both of can brought much improved sonics because of the cryo-treatment as well as the snug fit.
-IMO