Second that, life isn't SATC. Maybe women who are still living where they grew up, went to school etc have these 'friendship groups' but harder for women that left home.
Assuming you are single, I can see how at a certain age friends can drop off, people that couple up and have kids then to keep to themselves and not be as available anymore.
Girlfriend-wise I have swapped my marriage-and-kids friends that have very limited availability to friends I've met later in life that are more aligned to me in terms of lifestyle. A few girls from work that we click with and make plans with, a few I've met through activities and have similar values etc.
Honestly though my best friends are all men. Similarly, unless they couple up and get banned from socialising, I spend a lot of my free time with my male friends and it's really nice. I can be a bit intense in terms of wanting to have deeper conversations beyond everyday chit-chat and sometimes just have someone to properly open up to, and find that men have much more tolerance to that type of thing. Or maybe that's just what I'm used to.
it seems your problem needs more immediate solutions though. Do you know any people that you like and feel you'd get on with? Have you tried asking them to spend time together, maybe start with a coffee? Anyone in your family who could be a friend? Anyone who you used to be friends with and who you might want to rekindle the friendship with? Do you do any activities where you could meet friends, e.g. clubs? I've met two girls at my swim club this summer and we spend most Saturday mornings together now.