U3A Hawthorn might be worth a try. There's also a riding group out of Hawthorn Rec Centre on a Tuesday morning - normally about 20km with coffee half way, but at least it's some company and a couple of them might be up for more.
And welcome to the forum.
Another idea; see Dean at Bike Life on Auburn Rd. He had a women's list going for a while so he just might know of someone.