Super,
If your looking for different sizes of heat shrink "SHRINK TUBE" try Radio Shack, They have Packages with multiple Sizes in them and they Tend to be a bit stiffer than Most. If you can't find any Let me know and I can mail you some. I have truck loads of it. "AVIONIC SHOP" lol. (you are speaking on where the control rod passes through the "Guide" on the Tail Boom Right? or is it the horizontal fin/boom support/guide bushing? LMK if I can help..
Kevin