I've never heard of a bulk amount other than Festool large packs being offered. I wonder though if contacting Festool USA directly might result in something different. Likely not knowing their merchandising style, but still, I'd give it a try.
Insofar as doing it yourself, keep in mind the structure of a Domino and in particular its sidewall ribs, tey are thee for a reason. Replicating those essential sidewall ribs is the PITA that makes making your own a PITA and not worth it imo. Just spend the money is what I came up with.