If one was never circumcised can they be called up to the Torah for their bar-mitzvah?
As with all questions of practical halachah, CYLOR (especially since there may be public policy issues involved). However:
Responsa Hillel Omer (Yoreh De'ah 144) addresses such a case. He says that the boy is certainly allowed to have an aliyah, considering that it's not his fault that he is uncircumcised; at that age the responsibility still rests on his father to arrange it.
In a different context, R. Moshe Feinstein (Igros Moshe, Orach Chaim 2:32:2) states that an uncircumcised kohen should still be called up first to the Torah, since after all he is a full-fledged Jew and kohen.
Naturally, considering that a bar mitzvah is supposed to be a celebration of the boy's responsibility for and acceptance of mitzvos, then if a bris can be arranged before the bar mitzvah - obviously, assuming that it is medically possible (that the boy isn't a hemophiliac or the like) - then so much the better; make it double celebration!
See also Melamed leHoil 2:79 from Rav Hoffman of Berlin who wrote that min hadin it's mutar, however, according to the circumstances it might be reasonable not to do so.
The rabbis of the city have the right to introduce such a restriction. See there regarding specific details of how they realized this exactly.