Mike,
If you can find the approximate date of purchase (did you e-mail them) then you can contact the supplier and ask for a copy of the invoice. They are required by law to keep invoices on which they have charged, or been charged, VAT for seven years. They are not obliged to to supply you with a copy, but if you imply that you have claimed the VAT back as a business expense and you cannot find your invoice, and that you have an inspection by HMRC looming, they may be more likely to take the trouble to send you one. :wink: