RS485 is an electrical signalling standard, so it just describes a particular way of indicating both logic high and a logic low over a 3-wire cable.
The 'protocol' that's used specifies how the signalling standard will be used to convey data between two or more devices. Nearly all the protocols carry payload data in byte units, though there's few scattered about that don't.
It sounds like the device you're talking to uses some quite particular protocol but you don't give any details, so it's impossible to answer your question: is there a standard IC to encode and transmit switch positions in your device's protocol.
You could, as has been suggested, effectively produce your own converter IC, by using a microcontroller and writing your own software for it. But since you're specifically looking for a standard IC, I imagine that isn't something you feel capable of doing. And it is a fair-sized undertaking if you've not done anything like that before.
So, to start with, have you got some specific details of either the protocol or the target device you're looking to transmit to?