I used to live and San Diego and made Tijuana my second home. First of the place is mad dirty and mad dangerous, if I had a choice I'd head an hour south to Rosalita, where you can actually chill on vacation, go to the beach with out bathing in industrial waste,and get weed more safely.But if your'e intent on getting some in TJ, DON'T ASK FOR A POUND!! you will either end up having to pay large bribe money to the policia to keep out of jail, or robbed rolled and left in a gutter, becuase if you ask for a pound they know that you have alot of money at once. The best way I've found was to go to a club (ie Animal X etc) thats friendly to americans (watch out for Adelitas though, your girl would not be happy if you ended up there ) and after you pay to get in ask some of the patrons or bouncers. You can also score from the touts (these are the guys that walk up to you on the street and ask what you need) They throw in a middle man price of and added 10-20 dollars usaully though. Only buy in Oz or less amounts to help protect yourself and never NEVER get in a car with someone to go pick it up. The city is run by ruthless drug cartels whose main business is coke exports across the US border.
But once again I would suggest riding an hour south to Rosalita and just buying it off a friendly face on the beach as its readly available, cheaper and better quality usually.