DO NOT RUN ANY PLUG EXCEPT R4118S-9!!!!!!!
You can get that plug for 7.44 US Dollars at
www.sparkplugs.com
Use part# R4118S-9 to find it on the site. Great company to deal with.
You also need to look into reasons why you are fouling so many plugs.
I have not fouled a plug in any of my 2 strokes in over 10 years.
Plugs foul for a reason.
Make sure you have correct jetting, clean out the carb, correct fuel mixture ratio etc etc....