I have just come across a website about visiting gardens and accessibility. They have a directory whereby visitors can comment on accessibility as a guide for others. They are looking to expand the directory too. I think this is a brilliant idea as one thing you do have to do when you are out and about is to prepare. We have found is that an able bodied persons idea of 'not far' might not be our own.
Its free and is run by a lady who is a garden designer who now has physical restrictions.
If anyone is interested just google Accessible Gardens.
The other thing that I have been doing recently is contacting owners beforehand to ask about accessibility. It has been really useful and has provided things like key codes to open gates so that we can continue on a circular walk with the mobility scooter.