Sam’s Club seems to be able to still get it, and it can be ordered from the manufacturer. Most of the wholesalers have stopped carrying it, and Canada has shut it down completely. Apparently in 2016 they had a disagreement with the guy who actually owned and understood the formula, so the product currently labeled VSL #3 is an imperfect copy of the original, well-studied formula. It seems to still work for me, and that’s the product my insurance company covers, so I’m sticking with it as long as I can get it.
The original, well-studied formula is now being sold under the name Visbiome, which (at the time of this writing) has an ad on this forum, along the right side of the page. Availability has reportedly been a bit spotty, but will likely improve.
There have been other discussions of this here, so a search on this forum for “Visbiome” will tell you more.