Generally, a knight would recruit his own squire however, from his network of contacts.
Darren's suggestion is one way, though that is a real crap-shoot, and you are unlikely to find someone skilled enough to be able to be of much use to you. Another option would be to take on a relative - a young cousin perhaps, or a young relative of your wife? You can just declare that if you wish. They'll be 15 years old.
Or you could go to someone like Sir Amig and ask about likely candidates. He is an experienced knight and would give you a good candidate. They may be a little older, and possibly more skilled.
With every knight in the county in Sarum (and most of the knights of the kingdom here as well), you have plenty of opportunity to network and pick one up. If you wish to take that route, go ahead and make a social skill roll of your choice, and we can see what you come up with.
