display the duplicate record on an acces form

I have an access 2007 form that is based on a query  dealer_trade_expo

SELECT dbo_dealer_trade_expo.accountnumber, dbo_dealer_trade_expo.dealername, dbo_dealer_trade_expo.businessname, dbo_dealer_trade_expo.address, dbo_dealer_trade_expo.address2, dbo_dealer_trade_expo.city, dbo_dealer_trade_expo.state, dbo_dealer_trade_expo.zip_code, dbo_dealer_trade_expo.phone, dbo_dealer_trade_expo.fax, dbo_dealer_trade_expo.email, dbo_dealer_trade_expo.salesrep, dbo_dealer_trade_expo.attending_day1, dbo_dealer_trade_expo.attending_day2, dbo_dealer_trade_expo.special_event1, dbo_dealer_trade_expo.attending_day3, dbo_dealer_trade_expo.attending_1, dbo_dealer_trade_expo.attending_2, dbo_dealer_trade_expo.attending_3, dbo_dealer_trade_expo.attending_4, dbo_dealer_trade_expo.notes, dbo_dealer_trade_expo.Date
FROM dbo_dealer_trade_expo
ORDER BY dbo_dealer_trade_expo.Date DESC;

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the data is entered in to the table by both an access form and from a web form on our web site, I have a check on the access form to prevent duplicates from being entered but I don't control the web form and duplicates are being entered, I would like to display the account number of the the duplicate records on the form or a message box that displays the duplicates so they can be deleted, but not sure how to do it.