These spring covers are suitable for your trampoline:

Pad for 305cm Froggy PRO Trampoline - Green
  67,10 
In Stock
305cm Froggy PRO trampoline safety pad/spring cover. Buy
Protective Spring Cover for Trampoline inSPORTline Flea PRO 305 cm
  67,10 
In Stock
Protective spring cover for 305 cm Flea PRO trampoline. Buy