Isn't it a basic corollary of Calvinism that there aren't going to be that many Calvinists? The way is narrow, etc.
Nope.
1) As they say, in heaven everyone will be a Calvinist.
"Calvinism, simply put, is the conviction, derived from the Bible, that God is the ultimate source and final reason for our salvation in Christ." -- John Newton, author of the hymn, "Amazing Grace."
2) God has elected His children from among all nations and races and eras. While each name has been ordained by God the total number is vast and includes a multitude of believers; as many as God has chosen to redeem by Christ's sacrifice.
"Let there be no misunderstanding at this point. The Arminian limits the atonement as certainly as does the Calvinist. The Calvinist limits the extent of it in that he says it does not apply to all persons (although as has already been shown, he believes that it is efficacious for the salvation of the large proportion of the human race); while the Arminian limits the power of it, for he says that in itself it does not actually save anybody. The Calvinist limits it quantitatively, but not qualitatively; the Arminian limits it qualitatively, but not quantitatively. For the Calvinist it is like a narrow bridge which goes all the way across the stream; for the Arminian it is like a great wide bridge which goes only half-way across. As a matter of fact, the Arminian places more severe limitations on the work of Christ than does the Calvinist..."