POLARIS (imazapyr) is available in 1-qt containers (enough for roughly 32 gal of spray-mix at a 3/4% solution).
Imazapyr is probably better than glyphosate for treating hard-to-control perennials (fewer applications required), but be careful not to use it in terrestrial sites that may harbor the roots of desirable trees since it is soil-active (available for root-uptake).
Also, IMAZAPYR 2SL is available in 1-gal containers, and is formulated with a surfactant included (unlike POLARIS).