i use 1/16 for JLTO, it fits tightly enough that you dont need to shrink it. for tjets or aftermarket shoes (like bsrt 504s) i use 3/32, which does need to be shrunk. i have bought mine at an R/C hobby shop, as well as online at mcmaster carr.
I have tried the shrink tubing on a few occasions and I have never seemed to be able to get it right, they always ended up tearing or pushing themselves off. I finally found me a flat ended set of hobby pliers which are just slightly wider than the pickup shoes and doing the foldover trick is now a snap.
I tried the shoe bending also but either ruined a lot of shoes or found that the adjustment wasn't correct. My solution has been much easier for me. I take a wide rubber band and cut approx. 1/32 cross section. I then hold the strip down and using an x-acto knife I cut a slit in the center. And now I have custom flat "rubber bands" that will fit over the ends of the pickups.
Next step is to adjust until you get the correct fit and travel. I have learned to cut strips with a narrow slit for t-jet pickups and a wider slit for tyco, etc.
Free, simple, and I haven't ruined a pickup. Give it a try and let me know what you think.
Thin strips of electrical tape work for me. It's sticky enough to hold in place but is still adjustable. By the way, thanks a lot for reminding me about this as I had been doing this last year but left it out of my recent TJet tweakings. It's a must on some cars.