i primarily use instagram to buy/sell/trade but the tags are kind of messed up now. tag accounts are really helpful: search [grp name] tags on ig or use #[grp name]sale/trade/wts/wtt etc. Alot ppl also use twitter where u can search [grp name] sale/trade/wts/wtt as well. I also live in a big city that has trade sell events which are a great way to get cheap pcs and save on shipping! I also use overseas sites sometimes like bunjang, mercari japan, and xianyu bc some pcs are much easier to find on there but that might be a bit much for a new collector, it would be better to join a group order for those to start with.