quick google search found the thunder tiger part # available on ripmax.com
judging by what it is, i would GUESS that it is a 1.4x prop, ie the pitch is 1.4 times the diameter, which is common for fast electric boats. in that case any 4mm 40mm 1.4x fiber reinforced plastic prop will work, or for a little more speed, something with identical specs made of bronze would work. my problem is, being from the land mass i am from, all the sources i know of will be for a propeller with a 3/16" bore, not 4mm.