The only place I know where loaded 20 vartarg ammunition can be purchased is
Hendershots. When I first made my 20VT, I purchased ammunition from them. It was made in house so it was not considered factory ammunition. There was really no accuracy to speak of, 1" or so at a 100 yards. And not all the ammunition would chamber since the neck had not been turned to match my chamber. There wasn't a headspace problem and no primer issues. I only purchased a small amount around 20 rounds I think. The few that wouldn't chamber were taken apart and the components were reused.