Where can I purchase the anti-snoring insert?

Oral appliances to treat snoring work by pulling the lower jaw forward during sleep. While these devices can be quite effective, they can also cause serious problems with your jaw joint and teeth, Therefore, a professionally-fitted device is recommended over a cheap "boil and bite." Regular follow-up to minimize the risk of jaw joint disruption, shifting of the teeth, or change in bite is recommended.

You would need to see a qualified dentist, preferably a Diplomat of the American Board of Dental Sleep Medicine. An untrained dentist would not be familiar with the potential side effects and how to treat them, and would likely not follow your treatment up with a sleep study. This is also the problem with online mouthpieces. Your snoring might be solved with an appliance, but something called "silent apnea" could ensue, so you need a follow-up sleep study to assess the efficacy of the treatment, regardless of what it is.