My mate is in fits over a fabulous '40's style frock she found in Tesco/Asda!!
She is wonderfully curvy and thrilled with the cut! It's a brown-white-white-spots number
Hope you find something; Dressing up a cheaper garment with out-of-this-world jewellry and/or shoes is a great way of making it appear more expensive. And don't forget to go all-out on some amazing lingerie - this is your anniversay after all!!
If you have a bit of cash then look up Vivien of Holloway online for some rather amazing 1950's full-skirted dresses as an alternative?
Fingers crossed!!