Reddit mentions of NTE Electronics 47-20306-CL Heat Shrink Tubing, Thin Wall, 2:1 Shrink Ratio, 1/8" Diameter, 6" Length, Clear (Pack of 30)

You could make a welded loop yourself if you like them that much.

All you need is a $15 heat gun and some polyolefin heat shrink tubing.
https://www.amazon.com/NTE-Electronics-47-20306-CL-Shrink-Tubing/dp/B007Z7XJG8/ref=sr_1_1?s=industrial&ie=UTF8&qid=1491228762&sr=8-1&keywords=clear+polyolefin+heat+shrink+tubing

The front 2 feet or so of any floating fly line is a level taper to give you a section to cut into as the line ages. To make a welded loop to loop connection, use a razorblade to slice the end of the fly line on a bias (about a 60 degree angle works best). Slide the tubing on the end of the line then fold the tip over and insert it back. I'd recommend about an inch of fusion space for max strength, but cut the tubing a little longer so you have working room, especially on the line-side, where you need the best fusion to keep the tip of the loop tacked down. Leave about 1/4" sticking out the end as the loop -- it doesn't need to be too big.

Two things are needed to fuse PVC fly line: heat (to liquefy the PVC jacket, but not so much as to scorch it) and pressure, which is what the heat shrink tubing actually does. (I am getting this info directly from the 3M lab technicians, by the way).

Using your heat gun, which is like a more powerful hair dryer, slowly waft the heat back and forth over the tubing. The heat shrink tubing will, well, shrink, thus capturing the PVC jacket of the fly line, which will soften and liquefy and then fuse. The tubing is more of a mold than anything. It just takes a little bit of practice and it is really not difficult. When it's all locked up, let it cool for 15 minutes or so then very carefully cut the tubing off using sharp tying scissors. It will unpeel pretty easily, leaving you with a factory-quality fuse.

I did a break strength test on these for Fly Rod & Reel a few years ago, and shockingly they are roughly three times stronger than a nail knot. (My home cooked fuses survived being pulled to the full 20 lb. break strength rated for the line core three times before failure. A nail knot failed at 12 lbs. of pull on average).

When a fused line fails, the way it fails is for the back end of the fusion to begin to separate and curl. That's why it is very important to get that section tacked how as strongly as possible, and also why the 60 degree cut helps at the beginning.

Have fun!