This is your career here and sometimes you must make sacrifices. In your department, there are some who think "if the department wants me to go, they will send me." To me they are like the wallflowers at the prom and will never get the opportunity to dance. Oftentimes your personal drive will have to take you there.
Invest Personal Time and Money in Training
So your agency has a limited number of instructors and not enough dough to fund that private DT class you have your heart set on. Take matters into your own hands. Don't wait for others to train you.