Somehow I missed the announcement nearly a year ago that SLA had a Twitter directory on the SLA Wiki. Only members can access the pages, but they list both individual SLA members and their twitter IDs and twitter IDs for groups/divisions/sections/etc within SLA.
You can see the lists here: http://wiki.sla.org/display/SLAINNO/Twitter+Directory (if you have an SLA login and password).
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