What a great find! I searched over 10 years to find the exact Smurf blue Earth Cruiser with the sand jam tires that I had as a kid.
I wish I had an easy source, but unfortunately they have stopped producing the seashell tires and those pedals. Parts do come up on eBay from time to time. I have also had luck on the BMX forum (got a set of timers and an "Earth Cruiser" seat). There appear to be people on this forum that have Sand Jam gear too.
Not sure where you are located, but complete Jamis cruisers seem to come up more frequently and for less $$ in the mid Atlantic and southeast. You might just buy a complete bike if it has good tires and pedals and do a swap. Good luck!