You can get 2oz refills and even huge 16oz bottles on Amazon. I have a 2oz bottle that I'm about 1/3rd the way through (16oz is kind of crazy big for a residential pool user).

Good luck and I'll keep an eye out for your CYA result. My fear is that your CYA is crazy high and 25ppm FC may not be adequate for a shock level. Also, when your pool is clear, knowing that CYA exactly will help you target a proper FC keep the algae at bay. If it's really high, your pool may warrant some water draining to help get your CYA down...not fun to dump water but the alternative for an over-stabilized pool is to run at a higher FC level which means more bleach and more frequent bleach additions which can be costly too in the long run.

First things first, get the pool sparkly again, then worry about stabilizer....