Is it just that size just can't fit for your bust?
Because I think you could get it custom made, most people on eBay do custom
Or you could actually get a binder to slightly decrease the size of your bust so you can fit into the sizes if they dont do custom orders. I hope that helps I have bought Lolita just cosplay but I'm sure it's the same principle when it comes to those sellers on eBay.
I'd be very wary of e-bay stuff. However! Fan Plus Friend and Anna House and quite a lot of Taobao places do custom sizing. You could also try commissioning something or checking around the egl_comm_sales.