I am in the UK and here it is quite easy to get 50mg pills in any chemist.

The most common brand seems to be Pro Plus but they cost a bit so I shopped around and found cheaper generic brands on Amazon.

The cheaper brands (apparently intended for sports) come in 200mg pills which I break in half with a knife.

These work fine, but one thing I discovered is that I need to remember to drink water as some of the symptoms of dehydration are similar to caffeine withdrawal.