UIPageViewControllerEndlessDataSource: provides an 'endlessly' scrolling wrapper for `UIPageViewControllerDataSource`. Is also rather simpler to set up.

UIPageViewControllerEndlessDataSource.h

//
//  UIPageViewControllerEndlessDataSource.h
//  Created by Jonathan Crooke on 02/04/2014.
//

#import <UIKit/UIKit.h>

/**
 *  This data source protocol provides a wrapper for `UIPageViewControllerDataSource`
 */
@protocol UIPageViewControllerEndlessDataSource <NSObject>
@required
/**
 *  Your data source must provide the total number of items to be displayed.
 *
 *  @param pageViewController The page view controller
 *
 *  @return Total count of pages
 */
- (NSUInteger) numberOfPagesForPageViewController:(UIPageViewController*) pageViewController;

/**
 *  Provide a page at the given index.
 *
 *  @param pageViewController The page view controller
 *  @param index              Index to be displayed
 *
 *  @return View controller for the given index
 */
- (UIViewController*) pageViewController:(UIPageViewController*) pageViewController
                   viewControllerAtIndex:(NSUInteger) index;

/**
 *  Your data source must be able to derive an index from a view controller.
 *
 *  @param pageViewController The page view controller
 *  @param controller         An already displayed view controller
 *
 *  @return Index for the specified view controller
 */
- (NSUInteger) pageViewController:(UIPageViewController*) pageViewController
            indexOfViewController:(UIViewController*) controller;
@end

/**
 *  Data source wrapper
 */
@interface UIPageViewControllerEndlessDataSource : NSObject <UIPageViewControllerDataSource>
/**
 *  Designated convenience initializer.
 *
 *  @param dataSource Data source object conforming to `UIPageViewControllerEndlessDataSource`
 *
 *  @return Instantiated data source to apply to `-[UIPageViewController datasSource]`
 */
+ (instancetype) endlessDataSourceWithDataSource:(id <UIPageViewControllerEndlessDataSource>) dataSource;
@end

UIPageViewControllerEndlessDataSource.m

//
//  UIPageViewControllerEndlessDataSource.m
//  Created by Jonathan Crooke on 02/04/2014.
//

#import "UIPageViewControllerEndlessDataSource.h"

@interface UIPageViewControllerEndlessDataSource ()
@property (nonatomic, weak) id <UIPageViewControllerEndlessDataSource> datasource;
@end

@implementation UIPageViewControllerEndlessDataSource

+ (instancetype) endlessDataSourceWithDataSource:(id <UIPageViewControllerEndlessDataSource>) dataSource {
  UIPageViewControllerEndlessDataSource *source = [[UIPageViewControllerEndlessDataSource alloc] init];
  source.datasource = dataSource;
  return source;
}

- (UIViewController *)pageViewController:(UIPageViewController *)pageViewController
      viewControllerBeforeViewController:(UIViewController *)viewController
{
  NSUInteger idx = [self.datasource pageViewController:pageViewController
                                 indexOfViewController:viewController];
  if (idx > 0) {
    // page back
    return [self.datasource pageViewController:pageViewController
                         viewControllerAtIndex:idx - 1];
  } else {
    // cycle to end
    NSUInteger num = [self.datasource numberOfPagesForPageViewController:pageViewController];
    return [self.datasource pageViewController:pageViewController viewControllerAtIndex:num - 1];
  }
}

- (UIViewController *)pageViewController:(UIPageViewController *)pageViewController
       viewControllerAfterViewController:(UIViewController *)viewController
{
  NSUInteger idx = [self.datasource pageViewController:pageViewController
                                 indexOfViewController:viewController];
  NSUInteger num = [self.datasource numberOfPagesForPageViewController:pageViewController];

  if (idx < num - 1) {
    // page forward
    return [self.datasource pageViewController:pageViewController
                         viewControllerAtIndex:idx + 1];
  } else {
    // cycle back to beginning
    return [self.datasource pageViewController:pageViewController
                         viewControllerAtIndex:0];
  }
}

- (NSInteger)presentationCountForPageViewController:(UIPageViewController *)pageViewController {
  if ([self.datasource respondsToSelector:_cmd]) {
    return [(id) self.datasource presentationCountForPageViewController:pageViewController];
  }
  return 0;
}

- (NSInteger)presentationIndexForPageViewController:(UIPageViewController *)pageViewController {
  if ([self.datasource respondsToSelector:_cmd]) {
    return [(id) self.datasource presentationIndexForPageViewController:pageViewController];
  }
  return 0;
}

@end