Mount Snowpeak is made up of various caves and pathways, not all of which are home to shopkeeps. You can find the locations of all the intrepid store owners on the mountain below.
You'll spot the Travelling Sales Plushie outside of the Crowned Champion's house. The Crowned Champion himself will also be selling goods, and will sell additional items to Master rank Paladins.
The Crowned Champion Gladstone's Paladin Life Shop
Secret Smithy Assistant's Blacksmith Life Shop
There is a Secret Smithy to the left of the first circular platform in Lava Cave. The Plushie assistant will sell extra items to Master rank Blacksmiths.
Mount Snowpeak Summit
Moley's Miner Life Shop
You can find Moley the Mole in the well next to the Royal Cabin. He will sell additional items to Master rank Miners.