In case you haven't seen it, since it's not very prominent: the search page @outsidecontext linked has a section to search by catalog number. What that does is start an advanced search for releases by catalog number.
That search ignores spaces, so you can do, say, catno:CHAN0644 to find Chandos Chaconne's CHAN 0644 release. You can also use the label in that search: label:"Chaconne". For some reason, though, a search of label plus partial catno doesn't seem to work: "label:"Chaconne" AND catno:0751" finds no results. Maybe @ijabz has some better ideas on how that one could be made to work.