-- somewhere in your addon's initialization
local myTooltip = CreateFrame("GameTooltip", "MyAddOnTooltip", UIParent, "GameTooltipTemplate")
myTooltip:SetOwner(UIParent, "ANCHOR_NONE")

-- later, when you want to look at a tooltip
myTooltip:SetUnitBuff("player", index of buff)
for i = 1, myTooltip:NumLines() do
    local textLeft = _G["MyAddOnTooltipTextLeft"..i]:GetText()
    local textRight = _G["MyAddOnTooltipTextRight"..i]:GetText()
    -- do a :match or whatever to look for pertinent text
end