My GUESS:
307: Unlikely they have parts. It has been out of production since Buck started making the 300 series in-house.
As you no doubt know, the 307 is 0.25 inch longer closed than the 301, so 301 blades probably won't fit. For sure they will not fill the blade well as much. Also, the current production 301 is a 3 spring design. The Camillus era multi-blade 300's were all 2 spring.
701: IF it uses the same blades as the 301 ... maybe they could do a blade transplant. I think the 701 was a 2 spring design, so the 3 spring 301 blades may not work since they are not kinked to clear the other blades.
"30? Possibly Cadet" that would be the 303, I believe. They MIGHT be able to do a blade transplant, if the pivot pin on the current production 303 is the same as the Camillus era 303, and the old knife does not have kinked blades.
Best you can do is ask Buck. Worst case they tell you they don't have the parts, and offer you a new 301 for the 307, and maybe the 701, and a 303 for the Cadet?
EDIT:
Be aware that if they can do a blade transplant the new blade(s) will have the current tang stamp and date code, and be 420HC not the original 440A that the Schrade family of brands used.