You can get cheap ones from China that usually work pretty well. See: [www.ebay.com]
Or VXB has LM6UU's for less than $7 each: [www.vxb.com]
Going to 8mm rods and LM8UU's is another option, just make sure that you are able to modify everything to work, such as the carriages.
Or VXB has LM6UU's for less than $7 each: [www.vxb.com]
Going to 8mm rods and LM8UU's is another option, just make sure that you are able to modify everything to work, such as the carriages.