So I can understand how it's possible to find something that's better quality than rat shack. But if one has no choice, one goes to rat shack.

There are lots of sources, but it's true that places like Graybar aren't usually around the corner the way Radio Shack is. There are lots of outlets on-line like Jensen Tools , but it's nice to get a look at the stuff. Marine supply outlets carry it but pricing varies from OK to ridiculous. Some hobby shops carry some, too.

In Loren's shoes I'd give the Radio Shack stuff a whirl. I think if you have a real heat gun and go gently, you may have a better chance of success. One of my observations is that I think the RS stuff denatures (or something like that!) if overheated and thus the deforming at the ends. I was too lazy to go get my heat gun when I used the RS stuff last and tried gently using a flame from wooden matches, but no-go.

Anyhow, Loren is going to do what I did, box-wise, but do it right! (so I figured my tubing rant might help)