"In the United States it occurs in serpentine in Pennsylvania (as at Nottingham, Chester County) and in South Carolina and Utah. In East Africa large deposits of meerschaum were found in Tanganyika, once known as German East Africa, and since 1964 part of the United Republic of Tanzania. The main deposit comes from the Amboseli basin surrounding the Lake Amboseli. Tanganyika Meerschaum is normally stained in shades of brown, black and yellow, and is considered to be somewhat inferior to Meerschaum from Turkey. The raw material was primarily mined by the Tanganyika Meerschaum Corporation and uncounted pipemakers throughout the world were supplied with Amboseli Meerschaum. Another variation of the meerschaum pipe is the Calabash Pipe made iconic by Sherlock Holmes. The calabash is a gourd similar to a squash, grown specifically for use in pipes. The shape is determined as the gourd grows by placing small blocks under the stem, forcing it into a gentle curve. The mature gourd is cut and dried, then fitted with a cork gasket to receive a meerschaum bowl. The finished pipe offers one of the coolest, driest smokes available." ~ Wiki
I'm assuming there are similar substitutes which are available in raw form. Also, you'd think it's something that would have been produced or could have been produced synthetically if there was a market for it. If it's used over seas as incense burners, having a synthetic equivalent for production purposes would be ideal, but maybe nobody has.
Reading all this has lead me to research pipestone. I'm from Minnesota originally, and "Pipestone, MN" is where large deposits of pipestone are known to exist. We even have the "Pipestone National Monument", which I've visited, to my dismay. Obviously, natives have been using pipestone or similar stones for pipe smoking for several hundred years. I would surely like to get a hold of a very nice pipestone pipe, as well as some raw pipestone to carve myself.