I’m using a Siemens S7-200 SMART ST40 CPU and I need to add expansion modules. The problem is that I don’t have any physical space available next to the CPU to mount them.

Is there any kind of extension cable, remote expansion adapter, or alternative module that allows the expansion units to be installed at a separate location away from the CPU?

Has anyone dealt with a similar situation or knows an official solution from Siemens?

There was an extension cable available for the original S7-200. I do not know the SMART range (Siemens refuse to sell it here). So perhaps you need to look in the SMART's System Manual. Or contact Siemens and ask them if the extension cable from the old range would work.

(EDIT)
I have found it for you.