You could try yard and groom and see what positions they have advertised.
At our stable in the Netherlands we take in riders from other countries all year long for training and competing for a couple of months up to a year. As long as they have proof of riding quality, good teamworkers and we have space, they can either pay for living+shows and get their own groom, or they help with the stable work and get their living and shows for free with some extra money. A lot of big show/dealing stables have the opportunity to take on foreign riders in Europe. Ask your trainer if he has connections overseas to get you in touch with a stable 😊 good luck!