RBK53 extension

Hello, I have bought a RBK53 kit 6 months ago. Now I want to extend it, but seems that the RBS50 satelites aren't available anymore. So I have a system which I can't extend anymore with the same satelites I have. What are the options? I want to use the same Orbi experience, so not having different systems to manage. The new satelite needs to be compatible with the routers and my 2 satelites from the RBK53 pak (1x RBR50, 2x RBS50).

Tried the netgear wifi extender, but really sucks!