Sending a large centrifuge to the ISS was considered, but the Centrifuge Accommodations Module project got cancelled as a cost-cutting measure:
In February 2001, the Bush Administration announced possible cancellation or deferral of certain ISS components to stay within a Congress imposed $25 B cap.  In doing so, the International Space Station received its “core complete” design with President Bush’s new “Vision for Space Exploration.” This new vision was tailored in a manner that created a “U.S. Core Complete” design and an “International Partner Core Complete” design in an effort to mitigate increased expenses involving the development of the ISS.  President Bush’s vision mandated U.S. research on the ISS to be restricted to this new “Vision for Space Exploration” in which NASA willingly complied thus cancelling the Japanese Centrifuge Accommodations Module in 2005.
Smaller centrifuges like the European Modular Cultivation System (with a 0.6 m diameter centrifuge, compared to the 2.5 m one planned for the CAM) are used on the ISS.
Installing a centrifuge on the ISS is a bit more complicated than adapting a fairground ride. A simple design would cause vibration in the ISS modules, destroying the microgravity environment you need for many experiments.