How to make a local value equal multiple parts?

Its quite simple, you just have to iiterate through every object in workspace. and check if it have the value.

for i,v in pairs(game.Workspace:GetChildren()) do
    if v:FindFirstChild("Purchased") ~= nil then
        localMouseTarget = v
    end
end

"v" would be an object, this might not work but it should, if it doesn't try making a table and inserting v into a table.

There is nothing for that, there is a loop though...

for _, v in pairs(workspace:GetChildren()) do
    if v:FindFirstChild("Purchase") then
        if v.Purchase.Value == true then
            local mousetarget = v
            print(mousetarget.Name)
        end
    end
end

looping and finding purchased through all the parts then finding if its value is true then making the "mousetarget" the part...