An internship is not to give you experience with the discipline, an internship is to give you experience with the industry.
To expect to have access to a code base as an intern is akin to an apprentice blacksmith expecting to be working on a sword (the most difficult item to smith) or someone learning in a kitchen expecting to be cooking meals.
An apprenticeship is to learn how the business works, what is expected, what habits make for success, and frankly, to do the jobs that nobody else wants to do. If you're in a kitchen, you're job is going to be more cleaning and taking out the garbage. If you're a blacksmith, you're going to be hauling coal and iron and stoking the furnace.
An apprentice to a baker is not going to be working on a wedding cake either.
Another important lesson you seem to be learning against your will is that there is plenty of things in a job that you have to do that are not glamorous, are not fun, and do not advance your goals. These are real world things that even grizzled old veterans of the industry such as myself still have to do to this day.
If there is a need for me to crawl on my hands and knees to run cables, I do it, and so will you, now, and in the future, which brings me to the next thing an internship teaches.
An internship teaches humility. You are going to be surrounded by people who know far more than you, are better than you, and may have little to no respect for you. This should be a humbling experience, and an important one because this will always be the case to some degree. You're going to have to ask for help, ask for opportunities and prove yourself at every turn until you've earned trust and respect.
THIS NEVER CHANGES
While I don't mean to be too harsh, the reality of the matter is that in order to benefit from the internship, you need to have your eyes and ears open, and your mouth shut. You literally know nothing of the industry and the people you are working with are getting less from you than you are from them. Respect the time and effort they are putting forth and eagerly absorb everything they teach you.
You can pick up code in a book or online, workplace experience is the real value of an internship.