HDCD cropped up in a few players and still does now in the aforementioned Oppos, also Cambridge Audio's BD line players past and present. The strangest machine to have one though was in a local electrical store up at Bruntsfield in Edinburgh; it was a (very) basic DVD player that was going for about £29.99.
Most commonly though, it appeared on universal players such as those offered in the mid-to-late 2000s by Arcam, NAD and Denon's excellent DVD-3930. Those clocked in around the £800+ mark at the time (though you'll snag one for about £100-200 in mint nick now - worth it if the going prices for the Oppos and Cambridge players are too rich for your pockets).
Most people find HDCDs by accident rather than design; the ones I have are mainly those on the Grateful Dead's releases - D1ck's Picks official bootlegs and their Rhino label remasters. The Joni Mitchell remasters by Joe Gastwirt are also HDCD encoded, although her original releases are every bit as good.