Just found out something interesting...
www.rc4less.com
Carries foam tires/wheels for the F103. Rears are listed as a 28 shore and fronts are a 43 shore. Not sure how that compares to other compounds. However they are located in the states, Georgia i think.
I've ordered from rc4less several times and have always had great service.
http://rc4less.com/advanced_search_r...c578917a925895