You can definitely fab up new harnesses, and since they are NLA, that's what we're going to have to do once these start giving up the ghost, which is going to be more often given that these are only getting older by the day.
Personally, I've had intermittent Christmas tree lights for the past 4 months. I was quickly able to figure out that it was the plug on the alternator end of it making an in intermittent connection rather than the alternator itself(which I had just replaced a couple of months prior). I've been driving it around as needed and, aside from the initial annoyance when the lights come on, I've experienced no other adverse effects. It's not ideal to be driving around like that but my 4runner has been acting up too so I've had to make it work. I found a new alternator-end of the harness on Amazon
here, and it comes with enough wire to hopefully fix my issue. I was never able to find a part number or a match for the other end of the harness though. It's up there on my to-do list so hopefully I'll have it done soon.
I believe a while back Tim considered making up some new harnesses for members here, but ultimately I think it was too cost prohibitive to do unless there was a significant amount of buyers. That was a while ago, I'd buy two if he were to make them now since I know they'd be quality and likely last the life of the van (with a spare *just in case*).