There is no "Meso Exchanger" for now.
You can buy 500m for 1 slime eraser. Just pm any GMs online.
They will sell to you. If not report them to me >
After you collected 50 slime eraser .
Go to El Nath and talk to El Nath's Storage Keeper to exchange rares.
50 slime eraser each.
Thank you for reading
Regards,
xSkuller