Welcome to the forum!
There are, of course, several different ways to approach this problem. The simplest hardware solution might just be z-wave repeaters/range extenders if your physical arrangement allows you to plug in 2 or 3 devices in that area between your two zones. As z-wave is a mesh network, any mains powered (not battery operated) devices you have in that dead zone will improve the signal transmission substantially. If you have need for switches or what not, you can install those, if not, a simple repeater will suffice. That would improve the reliability of the connection while maintaining a single z-wave network.
If that’s not an option and you really are forced to have two separate z-wave setups then I think the two solutions you’d likely see the the most support for in this forum are:
Have a second OH instance running on a computer in the second z-wave zone with it’s own controller. Then you can connect those two OH instances either via something like MQTT (you can find several pretty good descriptions of various similar setups in these forums from people who need OH instances running in different locations) or if you’re up for the bleeding edge, the new remote OH feature of OH3. OH3 is pretty solid at the moment and many people are already using it as their main instance, but it is not quite yet, technically a fully stable release (it should be soon). Nonetheless, because of this new remote OH feature many people are already using OH3 to solve exactly this sort of problem.
Have a second z-wave controller in the second zone plugged into a computer that shares the dongle across the ethernet to the computer running OH. This can be tricky, but if I recall at the moment there are a few working solutions out there; a forum search for socat or rfc2217 should get you plenty of hits.