I do see 9-pin to 25-pin converters, but it seems to me that there must be a good reason for all those extra pins.
The RS232 interface set was developed in when communications interfaces had a lot more variety in hardware control functions than they do today (or have had for ~40 years) and synchronous serial wire line communications channels were still very common. The DB25 connector was needed to support all the possible
signal functions, but even in my working lifetime I've rarely seen more than the basic set actually in use.
Only handful of the original set of signal lines do anything useful for run-of-the-mill
asynchronous serial communications purposes that remain in regular use, and that set can be implemented within a DB9 connector... so simple DB9 to DB25 adapters do work fine for all but the most arcane purposes.
Thank you Cannon for this mess
Cannon had nothing to do with it... it was IBM that popularised the use of the already existing DB9 connector for RS232C, with the advent of the IBM PC.
Unless the process control kit you want to interface to is extremely
old, you shouldn't have a problem.