Thanks for your interest! I got a couple bags of powdered Lion's Mane mushroom from an Asian herb shop downtown Toronto. I also got a big bag of dried (but not powered) whole Lion's Mane mushrooms from a large Chinese grocery store (T&T) also in Toronto. So you can find them around, typically in shops that focus on Asian foods. These formats require you to process the mushroom for consumption (boiling it for tea, rehydrating, cooking into a meal, etc...) Here's a recipe I posted a few weeks ago for a Lion's Mane and Chaga mushroom tea mixed with Coffee:
Mushroom Coffee Recipe

If you want to keep it simple and just take a capsule every day, I can't recommend Paul Stamet's products highly enough. He uses three forms of extraction (hot water, alcohol and fermentation) to get the highest number of active medicinal components possible. Here's his Lion's Mane supplement:
HostDefence Lion's Mane

If you want to take it as a hot beverage without the hassle of brewing it, the best you can get is the instant packets from Four Sigmatic. Just add hot water and you're ready to go. They have a variety, but these two are the best:
Lion's Mane Elixir/Tea
Lion's Mane and Chaga mushroom with Coffee blend