Would you like to make us some?
Making shackles is like splitting firewood, too slow on a homeowner scale to make it a profitable venture, I really wouldn't be able to make anywhere near my usual hourly rate making them homeschool.
But as something to do for yourself while watching reruns of MASH on a Tuesday night... there are certainly worse ways to spend your time. It's like knitting, for men.
I splice single braid and make brummel locks for outhauls and other rigging on my boats, and it's pretty easy. The lightweight shackle shown in bcp's video looks like a regular brummel lock loop, stabbed back thru the weave of a single braid line, with a monkey's fist knot on the far end. The heavy duty version could be made by starting with double-braid line having a vectran or dyneema core and a more durable outer, and just stripping the outer off the ends, or conversely just buying some cover or tubing of your own to slide over the single braid if you prefer a reinforced tubing cover.
Wife is in a phone conference at the next desk, so I can't be scrolling youtube right now, but I'll find some videos on all three operations and post later tonight. In the meantime, here's a few where the preview looked promising:
Of course, you can also make simpler versions, which while having a weak point at the knot, are still likely way stronger than anything you'll ever need, if made from line having at least 2x your required pull:
Note that the knot used in that simple version is a figure 8, not a simple overhand. Figure 8's are stronger and easier to remove than overhands.