Like many things in life, this would require "critical mass" for it to work at all. That is, you would need a huge amount of pilots always renting gear instead of taking their own, for it to be worth it for anyone to hold stock of harnesses/wings/reserves ready to rent out.

There's so few people looking to rent equipment, that it would not be worth it for someone to have a full set of equipment(s) ready to rent...

As for pilots renting their own equipment out, it's too fraught with liability for most people to want to lend their stuff to a random stranger... What if they have an accident and get injured? What if they equipment gets damaged? etc etc...

The only chance you have is to rent something from a school, but probably it will be an A glider or low B, with an Open harness etc..

I prefer to have my own equipment.
I feel more comfortable and confident. I rent a car on my vacation now and then but that’s different in my opinion. As a dealer i often rent out equipment but almost always to give pilots a week time to decide if the wing fits their wishes.