floyd mayweather takes on manny pacquiao in las vegas on may 2 .
but no tickets have been sold for the event at the mgm grand .
briefs are on sale on ticketing websites but the sellers do not have them .
less than 1,000 are expected to go on public sale priced from $ 1,500 .
mayweather-pacquiao weigh-in will be first ever with paid-for tickets .
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