From v5.0 onwards, all equipment merchants sell pioneer (aka ancestral) weapons and armors. The cost (in Shiny Crystal) depends on the item level (see below). Lv.100 pioneer weapons and armors can also be purchased with Lv.100 Polish x4 and x6 respectively. Unlike the old system that exchanges Polish for equipment, you can purchase any amount without cost increment.
The v5.0 patch replaces existing Lv.1-80 Polish (aka Glazium) for Shiny Crystals. See Patch Notes v5.0.3 for exchange rate. Bounty Hunter's Guild also offers 1 Shiny Crystal in exchange for 2 Normal Tokens.