A variety of propeller sizes will fit your drone, with blade diameters between 5" and 6". A brief review of propeller specifications and available choices is provided below.
The numbers that are most important are diameter and pitch; a reasonable text/video tutorial is available here.
We recommend three-blade, 5" propellers with a pitch of 4" (ish). Possible choices include these Gemfan Hurricane props that we have purchased for the course. However, other 5" units should also work, with pitch from 3.5"-4" and with an M5 centre hole diameter (to fit the drone motor shafts).
We do not recommend 6" propellers for your drone. They will work, but the clearance between the edge of the propeller and the frame is limited.