i like to remove splinters i can't pull out by applying melted pine pitch to the area. watch out - it might burn you, but it works really well.
also, foot soaks in astringent tea.. whatever you got around.. but preferably very strong like oak bark decoction or something will also help pull it out.
homeopathic silica is another reputed remedy. only used it one.. splinter left, but i dont know if it was the silica or not.