Is it the Topographic or Hydrographic Water Navigation map you are referring to?I do have the Hydrographic map I use for boating and fishing purposes.The number of the chart is 6035.This will show navigation for the entire Eastern Portion of Lake Nipissing including South Bay, Sandy Bay and Sunset Cove to which you are referring to.The distance from Sandy Bay/Sunset Cove to Beacon Island is approximately 1.5 miles.You would need a foot or so of good ice to drive a vehicle out there but a snow machine would be the safer way to go.
Below are some links to where you can research and purchase either a paper or digital Hydrographic chart of that area.
My WebpageMy WebpageMy WebpageMy WebpageIf you need any quick information off of chart 6035 let me know and I'll try to help out.