Is there a tool to plot locations within X nm of a position?
At least a couple of tools exist to search for airports beyond a certain distance from your departure point. You didn’t specify, so I will use mine: KHUA.

Using gcmap.com, search for near:KHUA beyond:50nm within:70nm to get a list of airports in the specified range.

To plot some of them on a map, place a few of those in a comma-separated list, e.g., KHUA,KGAD,KBHM,KSYI,KBNA,KAYX,M22,TN50,KJFX,KMRC,KAPT,KPYP,1M4,M22, and select the Map tool. Plot range rings with one or more lines in the Ranges box under Map Controls. I used


  50nm@KHUA
  70nm@KHUA


Click the Draw Map button to update your map.

The final result will resemble the image below.