Horse soc.or even the British Horse Database. However, I personally see little point in spending a lot of money in registering with societies which are not really relevant unless YOU feel it is an impressive selling point. If blood typing is not required then there is little proof that the horse is genuinely bred from the said lines anyway. Hope all this helps a little bit and please send me an email to let me know how you get on or what you decide to do.
Feedback is always interesting and useful.