The first version of AberMUD was written in B (by Alan Cox of Linux fame, amongst others), and has survived as a printer listing. Here is some information: https://github.com/larsbrinkhoff/abermud/tree/master/abermud1
The Canadian company Thinkage offers B tools for GCOS: https://www.thinkage.ca/gcos/product-uwtools.htm It's a spinoff from University of Waterloo which has a history of using B going back to when Steve Johnson, the author of Yacc, was there in 1973.