Tube Extenders

Where can I buy a good quality tube extender for a 5U4 rectifier tube?
I used the socket savers from the tubemonger for my output tubes (EL34 6550 KT88 KT90 KT120). Had no problems but I will say the female socket is extremely tight. Also the male pins are a bit thicker than some pins from new production tubes. I believe they were made from leftover Tung Sol stock when they were made in the USA. At least that's what they advertised when I bought mine