Q. When can I find business cycle data?

The Economic Cycle Research Institute has data back to 1948 for 21 countries.

For the USA, the National Bureau of Economic Research has data back to 1854.

Also see Business Cycles and Depressions: An Encyclopedia which may be found in the Pardee Library Reference Collection. The back appendix provides dates for the USA, Great Britain, Germany, and various other countries and regions.