None of us likes long paper applications. They take forever to fill out. Sometimes you just don't know if you are giving the information needed. Online applications are pretty much universal nowadays.
Another very useful resource is the Online Application page on the SSAT site. SSAT has compiled listings of hundreds of private schools in the United States and Canada. You can search for schools by name or type or location. Tons of information there.
Tip: Many schools have admissions deadlines in early January. You will want to have all the preliminaries such as visiting the school and interviewing as well as the SSAT/ISSE done well in advance of the deadline. Having said that, some schools have rolling admissions.

