Yes I've been looking at those! It's a great picture isn't it! Never seen a woman wearing top boot like that before. She looks pretty smart though!
Can't answer your question though I'm afraid. The only website I know for hunting boots is www.bestboots.co.uk and I don't think I've seen those on there.
My mum had some put on her boots, actually because the boots were too short. If you can find a decent boot maker or repairer he would be able to give you a price to add patent tops to your existing boots.