What qualities are you looking for? Does the candidate need a second language? How much riding?
We have a breeding/sales farm in the Netherlands, and the working student will be doing everything around the horse, so partly feeding/mocking and grooming, taking care of them and also assisting in the training. She/he wont be stuck in the stall! We currently have 20 horses to ride so best would be if he/she is already a more advanced rider. Our horses are of the better quality dressage sportshorses, so experience and a bit of bravery is welcome since they have high quality gaits, and sometimes with some spunkiness that comes with a quality young horse! Of course it is a very educational trip to the Netherlands, she/he will be the right hand of a fourth level judge/internationally known clinician, FEI rider! Minimum time is 3 months, and if it is a good fit staying longer and showing is possible. A hard worker is needed, since we are a busy farm so we need to get the work all done by the end of the day. When I am on the road with clients or away on a clinic trip they will be partly responsible for managing the farm, so a responsible, reliable and competent person is important.
I've had great experience with all our working students so far (I think we've had about 10 by now from around the world incl. the US, Thailand and Finland) and have always been contacted through our website or postings up here or on horsegossip (the latter has got a very good response even long after I had put it up so seemly these threads are actively searched through by applicants).
From your describtion though I doubt you'll find what you are looking for as it sounds more like a job for at least half a hired position from someone trained and qualified. Bear in mind WS generally come for the experience of learning and are by virtue of nature seldom experienced enough to hold a responsible position on a busy professional barn. While it's certainly attractive to be able to ride under an FEI trainer this position will attract mostly folk who are into promoting themselves in the sport rather than wanting to become an equestrian professional of any kind.
Not to say it wasn't fair to expect someone to be hardworking but I think you are expecting a lot from a WS. i.m.e. riders who are capable of helping with young horse training from start generally tend to be out for a paid position especially when they are experienced enough to pick up more responsible chores.
I think it's fair to expect a WS to do all kinds of barnwork but I would never expect a WS to replace a paid position or even half a paid position. We've been extremely lucky to mostly have vet students or equine scientist students because we have the vet business on the farm which seems to attract a lot of students. The riding aspect is more of a bonus to them as we are not a show barn.
I would assume it's more difficult if you are a full time training barn because nowadays the species of the dedicated but pennyless barnrat seems to be virtually extinct at least we get a lot less hard-working-type kids around here, all they want to do is ride and have fun 8(
Good luck in your search! I'd try horsegossip!
So far we have had several good working students from all over the world so we might have been lucky so far if I hear you....I have never heard of horse gossip so I will try it there. I also put it up on facebook and already got some nice responses. Thanks everybody for thinking with me.