Based on my own experience, there are a very few wild-eyed libertarians that support that. They have their own website and don't come to FR anymore.
George Bush's Amnesty is Open Borders and near unlimited immigration by definition. Under his Employer/Employee Matching provision there is no limit to how many Mexicans can be included in his plan unless Congress sets one.
Bush has already gone on record as saying he wants the legal immigration annual limit that currently stands at roughly 1 million to be raised at a multiple of what it is. Is it 2 million, 5 million, 20 million? Aside from putting up millions of American Jobs for sale on the world market Who Knows?
With Amnesty limits set at such an exceeding high level, for all intents and purposes, it is an open border, unlimited immigration policy. Those that support Bush’s Amnesty and others like it are either unaware its provisions (or lack of them) or are indeed advocates of open borders like you.
The ploy you in the CAL are trying to perpetrate is that if the annual immigration limit is say 10 million (1 billion?) per year you can always say that “technically” there is a restricting limit in place, therefore it's not an Open Borders policy. When for all practical proposes it is.