I had the same problem, where I live there are no fineliners. I remember there used to be because I had used them before for school projects, but for many reasons nowdays they seem to be virtually innexistent. It caused me to stall on the homework because I believed doing them with ballpoint was wrong, so knowing my situation is not a complete loss and I can keep doing the excercises is a relief.

I'll keep doing the excersices with ballpoint while looking for the recommended fineliners then. Thank you very much for this answer!