Gymnastic Bodies Foundation 1 has at least (I’m not finished yet) one ring exercise in the course.
It’s only a pull up therefore, you could easily improvise with other equipment but where would the fun in that be – it is a gymnastic course after all.
I purchased the Elite Gymnastic Gym Rings on Amazon for £20 – the price seems to go up and down a bit – the price at the time of writing is £23.99 (just make it £24 – does the .99 scam influence anyone? Sadly it does, Priceless: The Hidden Psychology of Pricing, hard to believe).
These rings are superb, great value and, assuming you have an amendable ceiling, very easy to hang.
You don’t have to take my word for it, let my kids tell you all about them and throw in a quick demo.