These aren't workarounds really, just a matter of finding out in which R package these functions live in. Once we know which package contains the function we need (e.g. CellCycleSorting()), we can use this function in one of two ways:
# Load the functions in a package
library(package)
function()
# Or access the function inside the package directly using ::
package::function()
I am not familiar with the function CellCycleSorting(), so you will need to find out which package contains this function and use one of the approaches described above.