After many years of using a set of ring compressors similar to Jeg's #555-80516 manufactured made by KD Tools, I wore out the 4" band and the replacement 4" band lacked the quality of the original. Although I wasn't initially sure about the design, I tried the adjustable compressor similar to Jeg's #778-6676. After taking a little time to work with the adjustable, I've been very happy with it. It's something of a pain to need one unit for the traditional 4" motors and another for LS1 and other small bores but I've had good luck with them.
There was a thread a few days ago that asked the same question about other engine-building tools. I either locate specific items I need on Ebay or hit an online source like
www.goodson.com or
http://www.precisionmeasure.com/.
It pays to spend a few bucks on higher end precision measuring tools.
Good luck,
c