I know that I've seen at least 1-1/2 pairs on ebay since 2016. No, that doesn't qualify as predictable, let alone readily available...or...holy-grail either, and that's the point. If there are 2 NOS pairs out there (and, realistically, there are probably way more than that) sooner, or later, they'll show up on ebay... for a price. At that point, it becomes a question of whether anyone is willing to enter the bidding war, if there is one. As I said previously, damaged originals can be repaired; it boils down to finding the talent needed and the price. The tradeoff will likely be time vs OEM perfection. Even NOS may need new chrome; the original chrome didn't always look that good and, lacking a base layer of copper, it wasn't durable.
Sticking with the purist-concours approach, HL ears are a sticky issue. The question, to my way of thinking, is whether, or not, you're willing to make them the lynchpin of the entire project. It's a matter of "when" not "if" acceptable K3-`76 HL ears can be had, along with "how much" and that gap is going to be relatively small, regardless of "how" you go about that.
IMHO, the turn OEM turn signals on these bikes take the top spot for bad design. Extremely difficult to repair when damaged and virtually guaranteed to get damaged. IOW, once you have that perfect set for your 100-point resto does it really make sense to install them for anything other than display purposes? At a minimum, I'd use shorter stalks...to get them at least partially out of harm's way. Flexible, polymer, stalks would be even better. Which segues nicely into a third option, custom/aftermarket front signals...bolt-ons. That opens up a lot of viable options, since the originals could be easily swapped at any time. Your local DMV isn't going to care if your front signals are not purist-correct, as long as they are present and functional. Obviously, you're the only one who's opinions count...your bike, your call. That said, if you're as itchy to get this project done as it seems, it is possible to do everything else, have the bike functional and concours-correct, except for the HL ears...either to bridge the gap between project completion and HL ear completion, or for practical reasons. I mean, with everything but those HL ears done, the bike will still be a lot nicer than it is at present, won't it? Make no mistake, over the years, many of my projects have been derailed for want of some unobtainium part, or other, too. I understand what you're dealing with. But, this isn't running gear...