You do not need a liscense to buy them in Canada, out of Canada dont bother as you need a business, importation liscenses and a whole bunch of other head aches.
Do a search on here for an age verification rep in your area, once age verified to be 18+ (which means you need to wait 2 years) you will gain access to the Buy/sell forums.
Saskatchewan Age Verifier! Contact for more Info.
http://airsoftcanada.com/showthread.php?t=174161 - Honour & Respect your fellow players! #Airsofthonourandrespect