Have you tried Evans-they're nationwide , i have been to lots of different ones and they all had womens bikes , you can test ride any bike in the shop too so is not like they only have a few you can try. If you have a poor reach then you probably do need a womens specific bike , not all women need womens bikes however.

I have and highly reccommend Bianchis , also the Trek Madone comes highly reccommended too , I am on another forum - RCUK Road cycling UK a lot and they always reccommend the Madone and also the Specialized Allez ,along with Bianchi Via Nirones for that price range.

I am 5ft 8 and have a 55cm i  dont know how tall you are but maybe that may give you some idea about sizing - some manufacturers seem to go up in even numbers , some go up in odd ones!

Anyway always have a road bike fitted as it is very important especially as the position on a road bike is very different to a mountain bike, my opinion -after riding both road and mountain bikes is that if you can only get one that fits perfectly it should be the road bike . Evans will fit you for a bike too.

 By the way welcome to the dark side- i entered the dark side this time last year and havent looked back, however like mountain biking , road cycling can get very expensive, very quickly!!!! Just ask my husband! 

Let me know how you get on