Usually a local dispensary will carry seeds but not all of them carry the seeds. You can purchase seat online but there’s always a chance that they could be confiscated due to the agricultural laws plus shipping cannabis across borders is likely a legal issue that would get the key seed confiscated if inspectors found it or know the packaging it comes in but that is a rare problem because the packaging is very discreet. The cannabis magazines 10 to have advertisements where you can purchase seeds. Seeds are not legal in the US.
drolson