To follow up on this, I found an amazon page to order more LT elastomers. The elastomer chart is here, and as Mark said, they're color coordinated.
White - #1 Super Soft
Gray - #3 Soft
Blue - #5 Medium
??? - #7 Firm
Purple - #9 Extra Firm
When you buy a LT Thudbuster you get one #3 Soft, two...