Its odd that the shanks on those metric bits are larger than 1/2" dia when both are under half inch. Eitherway, if you want to change your chuck out, take the one you have out now and see how it attaches. Then you will determine if that press can handle a larger chuck or not. Your best bet is to order it from a industrial supply catalog:

McMaster-Carr
www.mcmaster.com

MSC
www.mscdirect.com

Rex Supply
www.rex-supply.com

Mike had a very good idea on getting the shanks of the bits turned down on a lathe. If you can find a contact that would do it, its pretty quick to do. Other than that, I'd look at buying the same size bits with a different shank diameter so it would match your chuck on your drill press right now.