I'm sure you probably have seen this already, but the most recent
Zam comments seem to indicate that vendors in newer areas (Planes of Power and up) will have unlimited Vials, while older vendors were limited to two. May be worth popping into live and checking out a few of the older vendors, although its definitely possible that changes have been made over the years to these vendors.
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Live:
Nubben, Level 80 Rogue, formerly of <Silens Dauthus> now of <Dark Bane> (Mithaniel Marr)
P99:
Nubben, Level 16 Rogue