As above, equipment like this, when it is available for sale, will tend to come up on industrial auction or disposals lists.
Note that equipment like this only rarely comes up for sale used. This type of expensive, high-end equipment is typically bought by companies who will use them until they are dead or no longer useful.
They do occasionally come up in bankruptcy liquidation auctions, and very occasionally when a distributor is disposing of discontinued models. (E.g. I recently saw a major distributor off-load a bunch of Tektronix scopes - MSO series - after they were discontinued by Tek, in favour of their new models) - still $3k and up, though.
Also remember that buying at industrial auction is not for the faint hearted. Make sure you read all the rules very carefully - these are commercial contracts, so there is no consumer protection. Typical rules include paying a 10% deposit to bid, which you then forfeit if you pull out of the purchase; Auction fees of 15-20% to be paid by the buyer; Buyer to arrange all shipping by a specific date; Absolutely no refunds, no warranty and no returns.