You might need to be more specific. Like in the UK, there are thousands of horses for sale in France, some by private ads, others in dealers yards, many from breeders, etc. and a large proportion are selle francais. If you can ellaborate on what you want the horse for and what kind of horse (e.g. young competition horse, or safe hacking horse, etc.) it will be easier to get useful suggestions.
Movement of horses between the UK and France is fairly straight forward with many professional transporters offering frequent services so you should be able to get a good deal on a part load, but of course this is an extra cost to factor in.
Then again they do crop up in the UK market as well:
