All over Chinatown, they have 50mg. Some places will only sell 2 packs of 10 pills, some will sell more. Boots had 100mg, but their price was well over 2x what I paid for 50mg. (Boots required recording the sale with my passport). All in the past 20 months, as recently as last month. I have a specific purpose in buying it for a friend who has cancer, and the meds her doctors give her often don't relieve her pain between doses.
Personally, I've taken maybe 3 or 4 Tramadol pills when I had a toothache and needed an extraction or a root canal. I've found that a combination of Ibuprophen and Paracetamol work just as well (suggested by my dentist). But that's another topic for another thread.