We kinda went thru this with Cuba..

Russia bad.. but nato and America stacking russias border with bases and capabilities to hit Moscow in 5 mins = good

Technically, a country can purchase arms from any country it choose. It is wise for a country to sell and trade arms with a neighboring country so peace deals can be signed. The normal way of doing business like this is the two countries sign a deal stating neither country can use the weapons bought and traded on one another, so that is a peace deal.

capable of reaching America? yes, both countries border each other. sorry had to say that

If the US turns it's back on Mexico, then Mexico can go shopping for arms wherever they choose. They're called "peace deals" for a reason.

Well turn about is fair play and since the US has been running the war in Ukraine....