For many years, I have used Williams Shaving Soap, about $1.25 at the local drugstore. It is about a quarter of an inch too small to fit snugly in the mug I use, but it yields a decent lather. Now the local drugstore does not carry it.
I have visited all of the local stores that are more or less on my way to work. None carry it. I had a look at a couple of places near work that cater to the highly groomed and (mostly) young. Both sold shaving soap. Unfortunately, both sold soap that costs $30 the box, and that is too big for my mug. I do not shave to look like the young and highly groomed so much as to avoid looking like a bum, so I will not pay $30 for a disk of soap that I would have to cut down. One did interest me, both in that it was from Trumpers, which is where Evelyn Waugh got his hair cut, and in that it came in a little wooden bowl. If I thought that shaving with Trumpers soap would make my prose resemble Waugh's, I might buy it. And every expended pair would offer two bowls to clap together in the manner of a Monty Python squire.
Today I found a drugstore that had not shaving soap but Deluxe Shave Soap, which I recall is what I bought last time. It had only one box, so in another few months I may have to undertake the same search.