Lead Screws may be purchased directly from Chinese suppliers on Aliexpress.com. From experience it takes about 2 weeks until delivery and i would recommend going this route.

 

They will send you a drawing; see above for you to specify the dimensions. The end part dimensions (bearing block end), need to be checked to fit the bearing blocks you decide on.

The other end is machined to match the existing lead screw, and just pops into the original plan bronze bearing (on X Y Axis).

The bearing block shown in the photograph, consists of two bearings running back to back in housing. They come in many shapes and sizes. Mounting them is easy , you can set up aluminium plates in the 4 jaw chuck of a lathe, bore the hole to the correct size , then use follow  punches to mark and then drill the (Allen screw) mounting screws.

 

Originally I purchased some un-machined Thompson Sigor screw and machined it myself. It cut easily with tipped tools, but I would recommend having them made, as it not worth the effort.