I can't seem to find a drop table for a load I worked up in my Ruger bolt gun in .450 Bushmaster,
300 grn Hawk spritzer at 2100 fps.
Anyone know of a source?

There are many exterior ballistic calculators online. If you have the bullets velocity, B/C, sight line above the bore, the sight in distance, the range increments and max range it will write out a chart showing the bullet path as well as remaining velocity and energy.
Handloads.com Ballistic Calculator is one.
Leo