Does the caffeine have to be pharmaceutical? If it's safe in your circumstances to experiment, I'd look at tea, chocolate, and coffee or cocoa beans, broken into appropriate-sized pieces to give you the effects you need (using a precision scale to provide consistent dosage). Cocoa beans are quite delightful raw, and bitter but enjoyable roasted. (Roasted whole cocoa beans taste good chewed with almonds or hazelnuts.) Try a health food or specialty food store.

Since food isn't standardised, you might need to experiment with the dosage again each time you buy a new batch. Pills would be easier and more reliable, if they deliver what you need.

Good luck,
Maureen