I don't know whether there are any third party remotes that can work. The original equipment costs around HK$300. You may try your luck in getting a used one from Apliu Street.
I have a SR4300 and a SR5200 waiting to be sold. But I have to keep the remotes to make selling the amps easier.
I'm not in HK and would be returning until mid June. This does not work well for me. I would charge you more, for the time I have to be involved, than what you would pay to buy a new one, plus a deposit. I'm a very costly consultant. Sorry.
If you intend to keep your SR5200 for at least a year, my suggestion is still getting one you can keep. It will cost you only $1 per day.