Right now I don't think desynth is relevant enough to warrant catch up vendors :/

There's no new craftable items that require demimateria, and all the obtainable demimateria have low ilvl sources.

If you REALLY wanna level it, though, there's other ways besides MB - although MB is undeniably faster.

Tbh right now there's really low incentive to spend high amounts of gil in power leveling desynth - the most you get out of it is some moderately pricy higher level mats, but nothing worth investing a lot of gil into as you're going to spend a lot of time making it back.

PvP is a really great way to level desynth, as is using poetics/allied seals/centurio seals for gear to desynth. Granted this takes more time, but it's also less expensive.