Unfortunately quatech has no driver for the "virtual serial port" and i am unable to
find anything similar (other brands)
I have never seen any vendor for this type of devices that supplied an OS/2
driver.
There are at least a few. NEC I
think was one. As OS/2 was *THE* premiere faxing and voicemail system "back in the day" (and honestly, still is - if only manufacturers still made such hardware for it), there were a variety of cards - serial, modem, fax/modem, and voice modem - that supported OS/2. Sadly, most of those were "complete setups" so getting the card required getting the voicemail system or serial "controller" unit and external voice/fax box to connect to the serial output card.
OS/2 had been supporting up to 64 line serial/fax/voice/modem installations for ages (since OS/2 Warp 3.0 if memory serves) - something other operating system dont seem very capable of doing without a LOT of additional hardware/performance. A standard Pentium or Pentium II level machine sufficed "back in the day" - not so much anymore on Windows.
This, btw, is an area I always thought that Serenity/Mensys should have been aggressively pursuing since an ancient OS/2 fax/voice/com system still can outperform newer Windows systems. And all it would seem to take is a set of updated drivers for the newer fax/voice/com boards.
Some of the systems seemed very easy to use... some (like the faxing solutions) were not the most "elegant" (no eye candy, rather bland interfaces - like the versions of multi-modem/line FaxWorks Pro from way back when), but they were (a) quite capable, and in numerous cases (b) supported REXX scripting or C++ programming to interact with them above and beyond their standard feature set.
So,
yes, there are (were?) various boards that were supported under OS/2 for large numbers of com ports. And
no, it seems very difficult to find them now - or drivers for them - or support for them.
I guess, since current day availability is the issue, that makes your post spot on - though perhaps with a little digging, you can find something a wee bit older that suffices.