That company has been gone for a long time. From what little I have read, they made a good rifle back in the day.
Saw some old posts that mentioned Kittery Trading Post having some parts in stock.
But... those sabots will probably be made from the old Polymer formula. They would possibly lead to 'plastic fouling' in the barrel depending on the velocity you choose to shoot them.
I would wonder whether the plastic in those sabots was still stable. Many people don't realize that plastic is porous, as well as it has an internal "moisture" content. Which means it can dry out, and become, for lack of a better word, brittle.
I like to use full bore bullets whenever possible.
Would love to find one of the original sizing tools that Fred included with his early rifles.
My GA-90 in 45 cal doesn't have any problems using 45 cal bullets up to .458