Register the control using ~/Custom/StoreLocator.ascx to get it working. The control is built like user control and user controls (.ascx files) are registered with relative path to the .ascx.
Do you want to have your say in the Sitefinity development roadmap? Do you want to know when a feature you requested is added or when a bug fixed? Explore the Telerik Public Issue Tracking
system and vote to affect the priority of the items