There is a great company called 'From Nicky's Kitchen' which is ran by local mum Nicky.
I am sure that Nicky would love to help you, her cakes are delicious and Annabel wrote about her business a couple of weeks ago in a news email.

https://www.facebook.com/fromnickyskitchen

My friend Zeyneb has started a business producing really yummy paleo food (I know so, I tried it) so pls look her up as well on www.facebook.com/mypaleokitchenuk and you can also place orders via mypaleokitchen@hotmail.com. She's based in Whitton.

Hi,

Feel free to contact me on mypaleokitchen@hotmail.com
with any specific orders. Happy to do birthday cakes!

Follow us on https://www.facebook.com/mypaleokitchenuk
where you will find our menu for download.

We offer Paleo Convenience delivered fresh to your doorstep.

Hope to hear from you!

Apples and Bees on Battersea Park Road (opposite the Latchmere pub) sells Paleo bread and 'muffins' that they buy from a local bakery.
Perhaps phone them and ask if they can order a cake from the same supplier? Or get the name of the supplier and call directly?
It probably won't be cheap though! Their paleo bread is about £6 a loaf

Cakeology in Raynes oark 020 8127 5166 or www.cakeology.net
Great cakes!

Hi, where can I buy a paleo birthday cake for my wife's birthday close to Earlsfield?