I'm actually after the exact same thing myself.
Had some weed called "Willie's one hit Wonder" in the early 90s. . .that was the post potent stuff I've ever tried. One normal sized joint couchlocked me, AND my heavy stoner friend, AND actually made a third person pass out! It also has a sort of unusual floral scent. Been looking for more every since, and would love to get my hands on some seeds, or even a clone of the real McCoy.
This is everything I've been able to unearth on this strain:
-The strain itself supposedly traces back to a pre-Soviet invasion Afghan strain. Its different enough from existing Afghani strains, that some think it must have been grown up in the mountains or another geographically isolated place.
-Its been claimed that this strain can't be flowered outdoors without starting flowering indoors first. That sounds ridiculous to me, and doesn't make genetic sense, but there it is. Again, I've never grown it, but this is supposedly one of those rare strains that combines extreme potency, a good yield, and a decent flavor. Most of the indicas will only give you (at most) two of those three things.
-The "William's" refers to Williams Oregon, where what we know as this strain was originally developed going back to the late 1970s. Its been claimed that this strain is still being grown outdoors there by old-timers as an heirloom strain. Since this is an inbred line (rather than some clone-only hybrid cut), seeds "should" be able to be produced by local growers. So probably if you knew the right folks, or travelled in the right circles, you might be able to get some. Don't know.
-Dru, from Oregon, and author of "West Coast Masters" growing guide specifically mentioned this strain as the best of the indicas, and one of the only strains he grows. (That says something, I think).
-The difficulty to obtain seeds, means that despite the fact that this is an IBL strain, its also one of those strains that people are growing/trading as "clone only". So even though seeds may (or may not) be commercially available, the strain definitely isn't extinct. It also does turn up from time to time at dispensaries, again, proving that it still is out there.
-I know BC bud depot offers Williams Wonder seeds, but that outfit has somewhat of a mixed reputation, and I haven't seen any reviews of the seeds. So far as I know this is the ONLY commercial offering at this time claiming to be pure Williams wonder:
https://www.bcbuddepot.com/seed-list/bc-bud-depot/williams-wonder/
If anyone has actually tried growing these or the ensuing product, I'd love to hear about it.
-After nearly a seven year absence Reeferman has recently re-entered the seed game, but I don't think he is offering Williams wonder at this time. Regarding his earlier seeds, I've seen several internet stories about them. Some claim they weren't a good representation of the strain. Others claim he obtained a large amount of these seeds from some third party, sold them under his name retail, then never paid the original breeder for them. I don't know the truth of these rumors.
-DNA Genetics currently offers a strain called "60 Day Wonder" which it claims is a lowryder backcrossed to a Williams' wonder multiple times, basically to the point where its a reasonable rendition of an autoflowering Williams Wonder. I've heard various reports on this one. My conclusion on reading many many reviews is that its not fully stabilized, and isn't exactly like the famous strain, but at least some of the phenos are quite strong. Every report I've seen says this takes 72-75 days from seed to harvest, by the way.