Dang you got bad luck lol. Both my reptile stores have frozen of all sizes but only the one far away has live of all sizes. Not sure about the Petco or Petsmarts around here though since like I said I don't feed frozen. But like others said, in your case, I would probably just bump up either the feeding schedule or amount of mice per feeding til your snake gets big enough to take the smallest rats you can find. As for too big, most pythons can handle large stuff. Its boas that are much more common to regurgitate especially Surinames.