Hey There. I currently have a zigbee network setup using MQTT and Zigbee2MQTT hosted on docker
My coordinator device is the SMLIGHT-SLZB-06 Gateway Coordinator devcie (ESP32, and CC2652P). My network also has a few third reality zigbee smart plugs. My network is working fine and I am able to communicate to those plugs via the ZIgbee2MQTT interface
Now I want to find a device (or even make one) that will allow me to bridge data coming from these smart plugs (over zigbee protocol) to an RS485 stream, that could potentially go onto a PLC.
to visualize
Plug -----> Coordinator (via Zigbee)------>Zigbee to RS485-------> PLC or initial testing using computer (via USB-RS485 adapter)
i would like to hear any suggestions or resources
What is your end use?
What PLC do you envisage using? To. control what?
Where does HomeAssistant (an even higher level co-ordinator) fit in all this?
Are you using MQTT? Can your PLC tap into that too?
RS485 and ZigBee are both network layer protocols - what drives or bridges them?
What data from the sensors are you repackaging for your PLC, and how? How often? Triggered by what? You may need an automation at the application layer to push the data, or maybe even an integration for your PLC to pull the data instead.
A hardware or software or configuration solution? Some or all, or none.
Not enough information.
Please search Siphonaptera for enlightenment. 
See if this gives you an idea. It’s not exactly what you’re asking for, but it’s in the ballpark enough to get you started.
Secondly, ask yourself if you really need direct communication between zigbee to RS485 without any HA involvement whatsoever.
Basically, what you need should be already possible if you let HA do its thing:
Plug -----> Coordinator (via Zigbee)------>Zigbee to RS485 HA via Modbus -------> PLC