In the early hours of Sunday, May 13, they used chains to rip double-steel gates "like a prison cell" off a strongroom at The Auction Company Broadway ahead of the firm's May 19 sale.
Auctioneer Andrew Granger said: "We've put a page on the website with pictures of all the stolen goods and just amended the sale-day catalogue online to saying 'stolen' for those items, but left the description there - everything is on the website, so at least everyone knows about it.
"While we're down on silver we have lots of other good ones. It won't stop it."
Mr Granger added: "It's the first time we've been targeted. We had a preview evening last Friday when everything was out and I'm pretty sure they just came for a look. It is extremely aggravating because it takes a lot of time and effort to put these things together, then it's all catalogued, but apart from that when the vendors put things in they don't expect them to be nicked do they?"