Do you mean those which are in the list of abbreviations? If yes, then N is very difficult to obtain. Like you can order it from darknet marketplaces, but it will cost hundreds of pounds with a chance the customs will seize it or cops with a wide smile come to your house. Plus a lot of scammers. If you are not afraid, you can find all the necessary information in PePH. It is on this forum, you can use a search engine. Btw there are some cheap return tickets to Mexico for around 850 euro in June. If you manage to get some money, you can travel to Mexico to try to buy there N.
SN is very easy to obtain. You can just buy it on Amazon or anywhere else where you live. Should be high-quality, almost 100 percent. It is more difficult to obtain antiemetics, you will need them for SN method.
All in all, you have to read a PePH and you will get much information. Piece