Here are some tricks I use:
I always observe the office area (whatever type of shop that is requiring a business card) and look for brochures or anything with the business name on it.
I am also on the lookout for business cards just sitting random in the little holders on the counter..
If the associate says they do not have a business card, I walk over to the generic ones and hand it to him and say, "Oh. Here I found one. Can you write your name and number because I want to come back and deal with you." They are usually flattered and sign it right away
I find the newer associates don't think as quick on their feet, as the more seasoned employees. The seasoned employee more often than not, grabs a card from anywhere, if he does not have any of his own..
The reason I do this is so I don't leave empty handed or "panic" because I have failed to get a business card
If all else fails, he won't write his name on a scrap of paper, he won't give you a business card, then I go outside and take pictures of the building, submit to the MSC with an explanation. You can't be punished if all the above fails (usually)