Looking for extended chain for your bike now that you're getting the stretch? Look no further, here you have the DID 420D Chain that Honda used on the Stock GROM! Excellent quality from the best name in the business, backed by Hondas decision to use this exact chain on the GROM!
This chain is 132 links, and will need to be shortened using the Motion Pro Chain Breaker Tool, that is also available for purchase. The stretch is adjustable in length, so you will need to shorten the chain to fit whichever length stretch you chose.
for the stretch installation instructions
... It also shows how to shorten the chain for use.