I don't think you can buy lead free primers - but on the WIN NT cases in .45 acp the pocket the primer fits into is actually sized as a small pistol primer vs a large pistol primer ( which is why a NT case jams in most loaders ...).
If you still have some of the boxes - the box, in the small print, at least it used to say lead free small pistol primers ... on it . It was probably about 3 years ago when I happened to pick up some WIN NT cases from a local indoor range ......and jammed up my press on station one ... and realized I had a problem. I actually had a case of unfired factory WIN-NT ammo in .45 acp I had bought locally - and I took it back. The shop had no idea they were using small pistol primers on those factory loads ...
I wouldn't really recommend you try to reload a WIN NT case in .45 acp .
Lead is a problem - but if you have a good ventilation system and shoot CMJ bullets - you'll cut down on a lot of that airborne lead issue.
I'm nor aware of anyone currently offering lead free primers for reloading. I believe PMC had some for a short period, though I never actually saw or used them, but saw ads for them.
The lead free primers are more brisant than lead based primers, causing the move to small size primers and, in some, crimping them in place as well. Some were done with larger flash holes - at least before the move to small primers.