You don’t say where your company is based - therefore there’s no point in recommending recycling places if they are half a world away and transporting the materials there would cost more in fuel and resulting carbon footprint than the gains in recycling.
The majority of materials mentioned are easily recycled, you’re not dealing with plastics, so a simple internet search to find local recycling initiatives will solve half your problems. (also where recycling is concerned - local is always better)
The steel -depends on the grade and composition, but again a local forge will be able to help. generally the closer the better. - who supplies the stuff to you and would they take it back for reprocessing? That way they could deliver new and take away old, saving fuel.
With the leather my advice would be to come up with a complimentary product to your current business and turn the used leather into that - or find a local furniture manufacturer etc who’s happy to take it off your hands - again you don’t mention volumes - always handy when trying to calculate the viability of a recycling initiative.
Pitching green initiatives to management…prove it will increase their revenue/save money and become a marketing point (if not a usp) gaining increased loyalty from existing customers and winning you new ones. That’s the only way they’ll listen.