Your friend's opponent is very wrong, and was most likely trying to intimidate him. You cannot get disqualified for having a damaged sleeve and not being able to replace it. Almost all venues, especially something as big as Regionals will have sleeves for sale. You can also legally play without sleeves, though this isn't recommended as the cards can get damaged extremely easily. However, it should be known that it is allowable on extreme cases. You should also get a judge right away if your opponent is doing rules lawyering like that, or trying to intimidate you in any other way.