The story I've always heard him say publicly is that after filming ROTS, he asked the prop-maker to make him one, and he obliged. But, who can say?
Also, just in case anyone is interested. In the early 2000s, when episode 2 was in production, it became public knowledge that the episode 1 hero was gone, that's why they use chromed resin stunts so much in AOTC. When MR made their AOTC saber--which was one of their first products--they based it on a chomed resin stunt because that's what was in the archives at the time. However, when Steve and the other people from MR worked on the OWK TPM EE saber, the MR people started saying "No, the metal hero is in the archives, I've seen it." I think that at this point, they were referencing the Salt Shaker saber, which was made for ROTS, but never used. That's because the MR OWK TPM EE saber seems to have some of the Salt Shanker's proportions, but incorporates some of the TPM details. What I think happened is when they went to make the TPM EE saber, they had access to the salt shaker. But, since the RPF had already obsessed over some of the TPM details with upgraded Larbels and JediVic's saber, they incorporated some of those details into their build and essentially created a hybrid.