Not only are they used in production, new boards are still being made and sold today. Search for PC104, which specifies a common form factor and interfaces.
There are also adapters for connecting PC104 to ISA.
Re: PC/104: There’s actually a few different variations of it. The original one used an ISA bus, yes, but as new buses were developed, new “versions” of PC/104 were released:
* PC/104: ISA
* PC/104 Plus: ISA/PCI
* PCI/104: PCI
* PCI/104 Express: PCI/PCIe
* PCIe/104: PCIe