I'm from Canada and I work for a couple publishers who sell their ePub on iBookstore. We use a third-party aggregator to sell books through various bookstores and there's pretty much nothing special we have to do to get them on Apple iBookstore. I'm sure it will varies from an aggregator to another, but I would suggest taking a look at those if you want to simplify the whole process.
Unfortunately, I don't have one to recommend, as in Quebec there is one that all publishers use—made by a company called De Marque,
here is a link—but I have no idea if you need to be a registered publisher (or part of the "publisher's association") to sell through their service.
I'm sorry I can't be of much help, but I thought I would share my limited experience.
Good luck, and let me know if you have more questions about this particular aggregator.